diff --git a/src/commands/code_mappings/upload.rs b/src/commands/code_mappings/upload.rs
index d40d6427c3..3bd9f2fef9 100644
--- a/src/commands/code_mappings/upload.rs
+++ b/src/commands/code_mappings/upload.rs
@@ -2,8 +2,12 @@ use std::fs;
 
 use anyhow::{bail, Context as _, Result};
 use clap::{Arg, ArgMatches, Command};
+use log::debug;
 use serde::Deserialize;
 
+use crate::config::Config;
+use crate::utils::vcs;
+
 #[derive(Debug, Deserialize)]
 #[serde(rename_all = "camelCase")]
 struct CodeMapping {
@@ -30,8 +34,7 @@ pub fn make_command(command: Command) -> Command {
             Arg::new("default_branch")
                 .long("default-branch")
                 .value_name("BRANCH")
-                .default_value("main")
-                .help("The default branch name."),
+                .help("The default branch name. Defaults to the git remote HEAD or 'main'."),
         )
 }
 
@@ -57,7 +60,295 @@ pub fn execute(matches: &ArgMatches) -> Result<()> {
         }
     }
 
+    let explicit_repo = matches.get_one::<String>("repo");
+    let explicit_branch = matches.get_one::<String>("default_branch");
+
+    let git_repo = (explicit_repo.is_none() || explicit_branch.is_none())
+        .then(|| git2::Repository::open_from_env().ok())
+        .flatten();
+
+    let (repo_name, default_branch) = resolve_repo_and_branch(
+        explicit_repo.map(|s| s.as_str()),
+        explicit_branch.map(|s| s.as_str()),
+        git_repo.as_ref(),
+    )?;
+
     println!("Found {} code mapping(s) in {path}", mappings.len());
+    println!("Repository: {repo_name}");
+    println!("Default branch: {default_branch}");
 
     Ok(())
 }
+
+/// Resolves the repository name and default branch from explicit args and git inference.
+fn resolve_repo_and_branch(
+    explicit_repo: Option<&str>,
+    explicit_branch: Option<&str>,
+    git_repo: Option<&git2::Repository>,
+) -> Result<(String, String)> {
+    let (repo_name, remote_name) = if let Some(r) = explicit_repo {
+        // Try to find a local remote whose URL matches the explicit repo name,
+        // so we can infer the default branch from it. Falls back to None (-> "main").
+        let remote = git_repo.and_then(|repo| find_remote_for_repo(repo, r));
+        (r.to_owned(), remote)
+    } else {
+        let remote = git_repo.and_then(resolve_git_remote);
+        let name = infer_repo_name(git_repo, remote.as_deref())?;
+        (name, remote)
+    };
+
+    let default_branch = if let Some(b) = explicit_branch {
+        b.to_owned()
+    } else {
+        infer_default_branch(git_repo, remote_name.as_deref())
+    };
+
+    Ok((repo_name, default_branch))
+}
+
+/// Finds the best git remote name. Prefers the configured VCS remote
+/// (SENTRY_VCS_REMOTE / ini), then falls back to upstream > origin > first.
+fn resolve_git_remote(repo: &git2::Repository) -> Option<String> {
+    let config = Config::current();
+    let configured_remote = config.get_cached_vcs_remote();
+    if vcs::git_repo_remote_url(repo, &configured_remote).is_ok() {
+        debug!("Using configured VCS remote: {configured_remote}");
+        return Some(configured_remote);
+    }
+    match vcs::find_best_remote(repo) {
+        Ok(Some(best)) => {
+            debug!("Configured remote '{configured_remote}' not found, using: {best}");
+            Some(best)
+        }
+        _ => None,
+    }
+}
+
+/// Finds the remote whose URL matches the given repository name (e.g. "owner/repo").
+fn find_remote_for_repo(repo: &git2::Repository, repo_name: &str) -> Option<String> {
+    let remotes = repo.remotes().ok()?;
+    let found = remotes.iter().flatten().find(|name| {
+        vcs::git_repo_remote_url(repo, name)
+            .map(|url| vcs::get_repo_from_remote_preserve_case(&url) == repo_name)
+            .unwrap_or(false)
+    })?;
+    debug!("Found remote '{found}' matching repo '{repo_name}'");
+    Some(found.to_owned())
+}
+
+/// Infers the repository name (e.g. "owner/repo") from the git remote URL.
+fn infer_repo_name(
+    git_repo: Option<&git2::Repository>,
+    remote_name: Option<&str>,
+) -> Result<String> {
+    let git_repo = git_repo.ok_or_else(|| {
+        anyhow::anyhow!("Could not open git repository. Use --repo to specify manually.")
+    })?;
+    let remote_name = remote_name.ok_or_else(|| {
+        anyhow::anyhow!("No remotes found in the git repository. Use --repo to specify manually.")
+    })?;
+    let remote_url = vcs::git_repo_remote_url(git_repo, remote_name)?;
+    debug!("Found remote '{remote_name}': {remote_url}");
+    let inferred = vcs::get_repo_from_remote_preserve_case(&remote_url);
+    if inferred.is_empty() {
+        bail!("Could not parse repository name from remote URL: {remote_url}");
+    }
+    Ok(inferred)
+}
+
+/// Infers the default branch from the git remote HEAD, falling back to "main".
+fn infer_default_branch(git_repo: Option<&git2::Repository>, remote_name: Option<&str>) -> String {
+    git_repo
+        .zip(remote_name)
+        .and_then(|(repo, name)| {
+            vcs::git_repo_base_ref(repo, name)
+                .map_err(|e| {
+                    debug!("Could not infer default branch from remote: {e}");
+                    e
+                })
+                .ok()
+        })
+        .unwrap_or_else(|| {
+            debug!("No git repo or remote available, falling back to 'main'");
+            "main".to_owned()
+        })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::path::PathBuf;
+
+    use ini::Ini;
+    use tempfile::tempdir;
+
+    use crate::config::Config;
+
+    fn init_git_repo_with_remotes(remotes: &[(&str, &str)]) -> tempfile::TempDir {
+        let dir = tempdir().expect("temp dir");
+        std::process::Command::new("git")
+            .args(["init", "--quiet"])
+            .current_dir(&dir)
+            .env_remove("GIT_DIR")
+            .output()
+            .expect("git init");
+        for (name, url) in remotes {
+            std::process::Command::new("git")
+                .args(["remote", "add", name, url])
+                .current_dir(&dir)
+                .output()
+                .expect("git remote add");
+        }
+        dir
+    }
+
+    /// Creates a commit and sets up remote HEAD refs so branch inference works.
+    fn setup_remote_head_refs(
+        repo: &git2::Repository,
+        dir: &std::path::Path,
+        branches: &[(&str, &str)],
+    ) {
+        for (args, msg) in [
+            (vec!["config", "--local", "user.name", "test"], "git config"),
+            (
+                vec!["config", "--local", "user.email", "test@test.com"],
+                "git config",
+            ),
+            (vec!["commit", "--allow-empty", "-m", "init"], "git commit"),
+        ] {
+            std::process::Command::new("git")
+                .args(&args)
+                .current_dir(dir)
+                .output()
+                .expect(msg);
+        }
+
+        let head_commit = repo.head().unwrap().peel_to_commit().unwrap().id();
+        for (remote, branch) in branches {
+            repo.reference(
+                &format!("refs/remotes/{remote}/{branch}"),
+                head_commit,
+                false,
+                "test",
+            )
+            .unwrap();
+            repo.reference_symbolic(
+                &format!("refs/remotes/{remote}/HEAD"),
+                &format!("refs/remotes/{remote}/{branch}"),
+                false,
+                "test",
+            )
+            .unwrap();
+        }
+    }
+
+    /// Calls `resolve_repo_and_branch` with explicit args and a pre-opened git repo.
+    fn run_resolve(
+        git_repo: Option<&git2::Repository>,
+        explicit_repo: Option<&str>,
+        explicit_branch: Option<&str>,
+    ) -> Result<(String, String)> {
+        // Bind a default Config so resolve_git_remote can call Config::current().
+        Config::from_file(PathBuf::from("/dev/null"), Ini::new()).bind_to_process();
+
+        resolve_repo_and_branch(explicit_repo, explicit_branch, git_repo)
+    }
+
+    #[test]
+    fn find_remote_for_repo_matches_upstream() {
+        let dir = init_git_repo_with_remotes(&[
+            ("origin", "https://github.com/my-fork/MyRepo"),
+            ("upstream", "https://github.com/MyOrg/MyRepo"),
+        ]);
+        let repo = git2::Repository::open(dir.path()).unwrap();
+        assert_eq!(
+            find_remote_for_repo(&repo, "MyOrg/MyRepo"),
+            Some("upstream".to_owned())
+        );
+    }
+
+    #[test]
+    fn find_remote_for_repo_matches_origin() {
+        let dir = init_git_repo_with_remotes(&[("origin", "https://github.com/MyOrg/MyRepo")]);
+        let repo = git2::Repository::open(dir.path()).unwrap();
+        assert_eq!(
+            find_remote_for_repo(&repo, "MyOrg/MyRepo"),
+            Some("origin".to_owned())
+        );
+    }
+
+    #[test]
+    fn find_remote_for_repo_no_match() {
+        let dir =
+            init_git_repo_with_remotes(&[("origin", "https://github.com/other-org/other-repo")]);
+        let repo = git2::Repository::open(dir.path()).unwrap();
+        assert_eq!(find_remote_for_repo(&repo, "MyOrg/MyRepo"), None);
+    }
+
+    #[test]
+    fn find_remote_for_repo_preserves_case() {
+        let dir = init_git_repo_with_remotes(&[("origin", "https://github.com/MyOrg/MyRepo")]);
+        let repo = git2::Repository::open(dir.path()).unwrap();
+        assert_eq!(find_remote_for_repo(&repo, "myorg/myrepo"), None);
+    }
+
+    #[test]
+    fn resolve_no_repo_no_branch_infers_both() {
+        let dir = init_git_repo_with_remotes(&[("origin", "https://github.com/MyOrg/MyRepo")]);
+        let repo = git2::Repository::open(dir.path()).unwrap();
+        setup_remote_head_refs(&repo, dir.path(), &[("origin", "develop")]);
+
+        let (repo_name, branch) = run_resolve(Some(&repo), None, None).unwrap();
+        assert_eq!(repo_name, "MyOrg/MyRepo");
+        assert_eq!(branch, "develop");
+    }
+
+    #[test]
+    fn resolve_explicit_branch_no_repo_infers_repo() {
+        let dir = init_git_repo_with_remotes(&[("origin", "https://github.com/MyOrg/MyRepo")]);
+        let repo = git2::Repository::open(dir.path()).unwrap();
+
+        let (repo_name, branch) = run_resolve(Some(&repo), None, Some("release")).unwrap();
+        assert_eq!(repo_name, "MyOrg/MyRepo");
+        assert_eq!(branch, "release");
+    }
+
+    #[test]
+    fn resolve_both_explicit_skips_git() {
+        let (repo_name, branch) = run_resolve(None, Some("MyOrg/MyRepo"), Some("release")).unwrap();
+        assert_eq!(repo_name, "MyOrg/MyRepo");
+        assert_eq!(branch, "release");
+    }
+
+    #[test]
+    fn resolve_explicit_repo_no_match_falls_back_to_main() {
+        let dir =
+            init_git_repo_with_remotes(&[("origin", "https://github.com/other-org/other-repo")]);
+        let repo = git2::Repository::open(dir.path()).unwrap();
+
+        let (repo_name, branch) = run_resolve(Some(&repo), Some("MyOrg/MyRepo"), None).unwrap();
+        assert_eq!(repo_name, "MyOrg/MyRepo");
+        assert_eq!(branch, "main");
+    }
+
+    #[test]
+    fn resolve_explicit_repo_infers_branch_from_matching_remote() {
+        // --repo matches "upstream", --default-branch omitted:
+        // branch should be inferred from upstream's HEAD ("develop"),
+        // not origin's ("master").
+        let dir = init_git_repo_with_remotes(&[
+            ("origin", "https://github.com/my-fork/MyRepo"),
+            ("upstream", "https://github.com/MyOrg/MyRepo"),
+        ]);
+        let repo = git2::Repository::open(dir.path()).unwrap();
+        setup_remote_head_refs(
+            &repo,
+            dir.path(),
+            &[("origin", "master"), ("upstream", "develop")],
+        );
+
+        let (repo_name, branch) = run_resolve(Some(&repo), Some("MyOrg/MyRepo"), None).unwrap();
+        assert_eq!(repo_name, "MyOrg/MyRepo");
+        assert_eq!(branch, "develop");
+    }
+}
diff --git a/src/utils/vcs.rs b/src/utils/vcs.rs
index 948c35a0f9..2fd89b372d 100644
--- a/src/utils/vcs.rs
+++ b/src/utils/vcs.rs
@@ -301,19 +301,17 @@ pub fn git_repo_base_ref(repo: &git2::Repository, remote_name: &str) -> Result<S
         })
 }
 
-/// Like git_repo_base_repo_name but preserves the original case of the repository name.
-/// This is used specifically for build upload where case preservation is important.
-pub fn git_repo_base_repo_name_preserve_case(repo: &git2::Repository) -> Result<Option<String>> {
+/// Finds the best remote in a git repository.
+/// Prefers "upstream" if it exists, then "origin", otherwise uses the first remote.
+pub fn find_best_remote(repo: &git2::Repository) -> Result<Option<String>> {
     let remotes = repo.remotes()?;
     let remote_names: Vec<&str> = remotes.iter().flatten().collect();
 
     if remote_names.is_empty() {
-        warn!("No remotes found in repository");
         return Ok(None);
     }
 
-    // Prefer "upstream" if it exists, then "origin", otherwise use the first one
-    let chosen_remote = if remote_names.contains(&"upstream") {
+    let chosen = if remote_names.contains(&"upstream") {
         "upstream"
     } else if remote_names.contains(&"origin") {
         "origin"
@@ -321,7 +319,21 @@ pub fn git_repo_base_repo_name_preserve_case(repo: &git2::Repository) -> Result<
         remote_names[0]
     };
 
-    match git_repo_remote_url(repo, chosen_remote) {
+    Ok(Some(chosen.to_owned()))
+}
+
+/// Like git_repo_base_repo_name but preserves the original case of the repository name.
+/// This is used specifically for build upload where case preservation is important.
+pub fn git_repo_base_repo_name_preserve_case(repo: &git2::Repository) -> Result<Option<String>> {
+    let chosen_remote = match find_best_remote(repo)? {
+        Some(remote) => remote,
+        None => {
+            warn!("No remotes found in repository");
+            return Ok(None);
+        }
+    };
+
+    match git_repo_remote_url(repo, &chosen_remote) {
         Ok(remote_url) => {
             debug!("Found remote '{chosen_remote}': {remote_url}");
             let repo_name = get_repo_from_remote_preserve_case(&remote_url);
diff --git a/tests/integration/_cases/code_mappings/code-mappings-upload-help.trycmd b/tests/integration/_cases/code_mappings/code-mappings-upload-help.trycmd
index 01033d6915..7eec72d0c2 100644
--- a/tests/integration/_cases/code_mappings/code-mappings-upload-help.trycmd
+++ b/tests/integration/_cases/code_mappings/code-mappings-upload-help.trycmd
@@ -13,7 +13,7 @@ Arguments:
 Options:
   -o, --org <ORG>                The organization ID or slug.
       --repo <REPO>              The repository name (e.g. owner/repo). Defaults to the git remote.
-      --default-branch <BRANCH>  The default branch name. [default: main]
+      --default-branch <BRANCH>  The default branch name. Defaults to the git remote HEAD or 'main'.
       --header <KEY:VALUE>       Custom headers that should be attached to all requests
                                  in key:value format.
   -p, --project <PROJECT>        The project ID or slug.