The rings, measuring 25 metres wide and more than 11 metres tall, weigh three tonnes and were unveiled as part of London Mayor Boris Johnson's city wide 'Mayor of London Presents' programme.
Suspended above the bridge, the installation joins displays in St Pancras – erected last year – and at Heathrow, to welcome the hundreds of thousands of visitors expected in the capital over the summer.
Marking the final 30-day sprint to London 2012, the rings were last night illuminated for the first time, watched by Johnson and Locog chairman, Lord Coe.
Andrew Douglass, chief executive of the agency who masterminded the construction of the rings, said they would create "one of the most iconic images in the run-up to the Games", adding that Innovision was "honoured to have been invited to create and install them on such a treasured and famous building.
Boris Johnson said: "Glorious Tower Bridge is recognised the world over and, adorned with the famous Olympic rings, is the perfect choice to showcase what London has to offer this summer.
"With just a month to go, we are making our final preparations and want to ensure each and every person in the capital gets a flavour of the celebrations and feels part of the Games.
Follow Ben Hall on Twitter @BRProducers