Prime Minister David Cameron called it "great news" that Boris Johnson intends to stand as an MP at next year's general election.
Taking to Twitter while on holiday in Portugal, the PM described Johnson as a "star player" for the Conservative Party.
The Tory leader told his 740,000 followers on the social network site:
The Tories are hoping Johnson will bring his personal popularity with the electorate to the party's election campaign, perhaps influencing voters who are uninterested in politics.
The London mayor is also a two-time election winner in London, which is not generally a strong area for the Tories.
That contrasts with Cameron, who failed to secure an outright win at the 2010 general election.
Johnson is also routinely mooted as a potential Tory leader, which could prove a headache for Cameron if his party loses in 2015.