Cannot push local Git repo to Visual Studio Online project
As @EdwardThomson said in the comments, you need to set up basic authentication on your account.
Go to your profile, select the credentials tab, and then click the enable alternate credentials link.
Also in response to @flame-spotter's comment about there being no in-IDE push: there is, but perhaps not as obvious as it could be to get to.
In VS2013:
- Go to View > Team Explorer.
- Select your repo and click 'changes'. Commit any changes you wish then click 'sync'.
- You then get to an 'Unsynced Commits' panel from which you can push, pull, merge, resolve conflicts etc.
Aside from the slight annoyance getting there, it's extremely powerful.