London's Air Ambulance (LAA) has agreed a deal to finance the service's helicopter for seven years.
The charity, which is funded by a combination of NHS money and public donations, agreed a deal with Santander.
The LAA's Dr Gareth Davies said the cash would allow it to focus on finding new ways to enhance the service.
It began operating 24 hours-a-day in April last year and has attended almost 25,000 call outs since 1989.
Mr Davies, medical director and chairman of the trustees, said: "We are approaching our 25,000th mission and we would like as many people as possible to know what an amazing job the team does.
"London's Air Ambulance is a vital service that saves the lives of many who may not have otherwise survived the distance to hospital."
The air ambulance attended 1,741 missions, 410 of which were at night, in 2009 and 1,979 last year.
Typically air ambulance crews attend to the most serious cases in London, such as shootings, stabbings and the worst traffic accidents.