Sometimes it is necessary to combine 2 different Git repositories with preservation of both histories. In this example I assume that we only have one active branch (master) around that none of the files are duplicates.

Follow these steps

• Start with 2 fresh clones
• Switch into the repository you want to keep
• Add a remote that points to the URL of the repository you want to import

git remote add <tmp name of 2nd repo> <URL of second repo>

• Pull the second repo with

git pull <tmp name of 2nd repo> master --allow-unrelated-histories

• The repositories are now merged.
• If necessary move anything around with git mv
• Remove the second remote entry

git remote rm <tmp name of 2nd repo>

• Push the combined repository to the server.