Marcus and Boris will be the first to use two of thousands of new bicycles at a Barclays Cycle Hire station in the shadow of the city's iconic London Eye landmark.
Barclays Cycle Hire provides an affordable, sustainable and environmentally friendly transport network across the capital, introducing people to a more active life and one of the cleanest, greenest and quickest ways of navigating the city.
The scheme is expected to transform the way people make short trips around central London.
Available 24 hours a day, seven days a week, the capital's newest form of public transport stretches from Notting Hill Gate to Wapping, and from Regent's Park to Borough Market.
Those using the scheme from today will be able to hire one of thousands of cycles from docking stations which are based only every 300 metres apart in central London.
This means that cyclists will never be more than a couple of minutes away from a docking station in the centre of the city.
Barclays Group Chairman Marcus Agius said: "An extensive transport system with good accessibility is essential to the health of London's economy.
"By improving London's transport capacity we will help the capital attract investment and jobs.
"We are committed to working alongside Transport for London to ensure that the Barclays Cycle Hire scheme is successful, and are proud to be part of the cycling revolution."
Mayor of London Boris Johnson added: "Londoners have awoken to a new dawn for the bicycle in the capital.
"Overnight racks have been filled with thousands of gleaming machines that will transform the look and feel of our streets and become as commonplace on our roads as black cabs and red buses.
"My crusade for the capital to become the greatest big cycling city in the world has taken a gigantic pedal powered push forwards."
Barclays Cycle Hire was made available from 06:00 BST this morning and access is initially available only to members. Other users are expected to be able to pick up bikes in around four weeks' time.
When completed, the scheme will see 6,000 cycles and 400 docking points located across central London.