Merge two Git projects, keep history

I needed to merge two separate projects into one repository while keeping the full commit history from both sides. Copy-paste would have worked for the files, but history would have stayed trapped in the old remotes.

This approach adds the second repo as a remote, fetches it, and merges with --allow-unrelated-histories so Git keeps both lineages. I still refer to the repos as project1 and project2, with remotes at project1Url and project2Url.

Step 1: Clone the original repository

First, clone the repository of project1:

git clone project1Url

Step 2: Add the new repository as a remote

Next, add the repository of project2 as a remote:

git remote add project2 project2Url

Step 3: Fetch the commits from the new repository

Fetch the commits from the project2 repository:

git fetch project2

Step 4: Merge the commits from the new repository

Merge the commits from the project2 repository into project1. Point at the branch that holds the code you want (often main or develop):

git merge project2/develop --allow-unrelated-histories

Step 5: Fix merge conflicts

If there are conflicts, you will need to resolve them. In my case, this was mainly build files and scripts in the root of the repository. Most of the important code was in subfolders, so this was minimal.

Step 6: Push the changes to the original repository

Push the changes to a new branch for review before merging into the main branch:

git checkout -b feature/merge-project2-into-project1
git push origin feature/merge-project2-into-project1

Step 7: Clean up

Test your code to ensure everything builds and runs as expected now that it is all in one repository. Create a pull request and review all the changes to ensure nothing gets changed that shouldn’t be.

When you look at your PR, it will look like a lot of code has been added. However, if you look closely at the Git history of those files, you will see that the history has been preserved from the original repository. You can remove the temporary project2 remote once you no longer need it (git remote remove project2).

Conclusion

This is still one of the simplest ways to combine two codebases without throwing away history. Use it when consolidating services or folding a spike repo into the main project; open a PR so reviewers can see the merge conflicts and folder layout before it lands on the default branch.

Once the histories live in one repo, automated promotion helps: see automatic pull requests for GitHub Actions and Azure DevOps patterns, and using GitHub Actions if you are wiring CI around the merge.

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