The drive, called 'Get Ahead Of The Games', aims to raise awareness of transport "hotspots" primarily in London, but also in other affected parts of the UK. Created by M&C Saatchi, it will run across press, outdoor, radio and digital and is expected to be seen or heard a billion times by the UK public.
It will begin by focusing on congestion "hotspots", before moving towards highlighting alternatives and urging people to use that knowledge. Finally, it will switch to reminding people that the Paralympics will also affect transport.
A new website, Getaheadofthegames.com, and a new Twitter feed @GAOTG, also went live today, offering travel advice and tips.
Johnson said: "This campaign is key to the preparation and planning that will help everyone in London to profit from what promises to be a remarkable summer."
The various Olympic and transport bodies have been keen to stress the importance of the controversial Olympic Lanes to athletes travelling around the venues. Johnson insisted the lanes would not be "exclusively used by fat cats".
He added: "Sponsors have been told that the best and fastest way to get around our city will be, of course, to use public transport."
As well as the ad campaign, new pink "wayfinding" Games signage was also unveiled.
For more on the plans, read Marketing this week for an exclusive interview with Transport for London marketing chief Chris Macleod