Git: Merge a Remote branch locally

Question

You can reference those remote tracking branches ~(listed with git branch -r) with the name of their remote.

You need to fetch the remote branch:

git fetch origin aRemoteBranch

If you want to merge one of those remote branches on your local branch:

git checkout master
git merge origin/aRemoteBranch

Note 1: For a large repo with a long history, you will want to add the --depth=1 option when you use git fetch.

Note 2: These commands also work with other remote repos so you can setup an origin and an upstream if you are working on a fork.

Note 3: user3265569 suggests the following alias in the comments:

From aLocalBranch, run git combine remoteBranch
Alias:

combine = !git fetch origin ${1} && git merge origin/${1}

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Opposite scenario: If you want to merge one of your local branch on a remote branch (as opposed to a remote branch to a local one, as shown above), you need to create a new local branch on top of said remote branch first:

git checkout -b myBranch origin/aBranch
git merge anotherLocalBranch

The idea here, is to merge "one of your local branch" (here anotherLocalBranch) to a remote branch (origin/aBranch).
For that, you create first "myBranch" as representing that remote branch: that is the git checkout -b myBranch origin/aBranch part.
And then you can merge anotherLocalBranch to it (to myBranch).

Whenever I do a merge, I get into the branch I want to merge into (e.g. "git checkout branch-i-am-working-in") and then do the following:

git merge origin/branch-i-want-to-merge-from

Fetch the remote branch from the origin first.

git fetch origin remote_branch_name

Merge the remote branch to the local branch

git merge origin/remote_branch_name

Maybe you want to track the remote branch with a local branch:

1. Create a new local branch:

  git branch -b new-local-branch

2. Set this newly created branch to track the remote branch:

  git branch --set-upstream-to=origin/remote-branch new-local-branch

3. Enter into this branch:

  git checkout new-local-branch

4. Pull all the contents of the remote branch into the local branch:

  git pull

If you already fetched your remote branch and do git branch -a,
you obtain something like :

* 8.0
  xxx
  remotes/origin/xxx
  remotes/origin/8.0
  remotes/origin/HEAD -> origin/8.0
  remotes/rep_mirror/8.0

After that, you can use rep_mirror/8.0 to designate locally your remote branch.

The trick is that remotes/rep_mirror/8.0 doesn't work but rep_mirror/8.0 does.

So, a command like git merge -m "my msg" rep_mirror/8.0 do the merge.

(note : this is a comment to @VonC answer. I put it as another answer because code blocks don't fit into the comment format)