Require Pull Request in TFS
git, tfs, tfs-2015
Solution
You tagged your question with TFS 2013, and I think that what you strictly ask for is not possible.
But in TFS 2015 and VSO you can access a feature called Branch Policies under the team project settings -> Version Control -> Click your Repository -> Branch Policies.
Well there you tick Require a minimum number of reviewers per pull request. If it is important that other make the review, make sure that Allow users to approve their own changes is not checked.
I have written a blog post which describes it in more detail.
Problem
Pull Requests were recently implemented in TFS. Is there a way to force users to make Pull Requests, and have others review it before they can merge into a branch? I've tried restricting Contribute permissions to the branch for a TFS group, but that prevented them from merging through Pull Requests too.