TBWA replaced the incumbent on the account - The Union - which won a place on the Scottish Executive roster after the closure of Yellow M Edinburgh in August.
The account was put up for review in February by the Scottish Labour Party's head of marketing, Steven Lawther, who invited The Union, The Bridge and 1576 to pitch with ideas of how to boost the party's profile in the run-up to the Scottish elections. The Union dropped off the shortlist following its move to the Scottish Executive roster.
The campaign, the second for the party since devolution, is likely to focus on raising the Scottish Labour Party's profile and move away from a campaign launched in 1999 which attacked the Scottish National Party.
The Union-created ad slammed devolution strategy, which meant a total split from Westminster, and used a picture of Hitler's face on a banknote.
The win comes two weeks before the Edinburgh agency officially opens.
Gary O'Donnel is relocating from London to Edinburgh to be the managing director of the new agency.
The win bolsters TBWA/London's hold on the main Labour Party account, based in London, according to the chief executive, Garry Lace.
"All start-ups need momentum, and this win is a great founding one for the new venture," he said.