HSBC will be developing business-to-business, consumer and grassroots activity in the build-up to and during the rugby union campaign, which begins in May 2009.
The deal, reportedly worth £4m, means HSBC will replace Zurich Insurance, which sponsored the British & Irish Lions ill-fated 2005 tour of New Zealand, which the Lions lost 3-0.
Other brands that have put their names on the team's shirt in the past include Scottish Provident and NTL. The team has retained Adidas as its kit provider since 1997.
The British & Irish Lions will face newly crowned Rugby World Cup champions South Africa three times as part of the tour, making the 2009 tour a more lucrative proposition for HSBC.
The team will also face the likes of Highveld XV, Western Province and Blue Bulls at domestic level.
David Hodgkinson, group managing director and chief operating officer of HSBC Holdings, said: "The British & Irish Lions tour is the most prestigious name in a sport that has enormous relevance to our business, clients and our people.
"We look forward to working with the British & Irish Lions Committee, as well as some fantastic rugby."
Martin Johnson, former Rugby World Cup winning captain for England and two British & Irish Lions sides, said: "For the next Lions team to be travelling to South Africa to face the current world champions will make the tour one of the greatest and most exciting of the modern era."