The £43.75m deal will see the current crop of blue Barclays bikes, colloquially known as Boris bikes, repainted in Santander's brand colours of red and white.
The new sponsor is also hoping that a new nickname for the bikes, 'Santander cycles', will catch on, though by anyone's standards the new moniker is a bit of a mouthful.
Along with the 11,500 bicycles, the hundreds of docking stations, service vehicles, staff uniforms and membership keys will also be rebranded.
The deal will mark a seven-year partnership between the bike scheme's operator, Transport for London, and Santander, with the rebranded cycles to arrive this spring. Santander will also launch a new Santander Cycles app to help would-be cyclists locate their nearest bicycle. It wil also give Santander customers cashback on their credit cards.
Marketing activity will extend to 'family-focused events' and 'Cycle Champions' promoting the scheme across Santander's own London bank branches.
Santander UK's CEO, Nathan Bostock said in a statement: "he Santander Cycles Scheme is a great example of our commitment to supporting the communities in which we operate across the UK.
"We are committed to making the experience of using Santander Cycles as simple, personal and fair as possible."
Mayor of London Boris Johnson added: "As everyone knows, London buses, phone kiosks and post boxes are red. In Santander Cycles, we have a new red icon symbolising the Capital to Londoners, and the world. Santander’s marketing expertise will help us take the cycle hire cheme to a new level, and I am thrilled to welcome them."
Ex-sponsor Barclays, meanwhile, has launched its own marketing offensive, netting Alan Shearer to front its "spirit of the game" campaign.