The three-year deal will become effective from 7 June and see the West Ham United club shirt - branded with the XL.com logo - go on general sale on 16 June.
XL will have a significant presence at the Boleyn Ground, including a bespoke XL design covering the entire roof of the East Stand and branding on the state-of-the-art LED pitch perimeter advertising system during matches.
This will extend further with XL.com offering a range of promotions and competitions to West Ham United's supporters, both on matchdays and through web incentives and direct mail channels.
XL is the fifth largest travel group in the UK, employing more than 2,500 staff, with divisions also in France, Germany, and Australia. Since the company's founding in 2001, XL has offered its customers a broad-based travel proposition, from complete holiday packages to flight-only tickets on award winning XL Airways.
The group distributes flights and holidays through its travel portal, XL.com and through numerous wholly-owned travel operations including Aspire Holidays, TravelCity Direct, Kosmar, Freedom Flights, and Excel Holidays, and in France; Vancances Heliades and Crystal. XL.com was launched in early 2005 and is one of the most visited travel websites in the UK.
XL's ensemble of 41 aircraft operates of the most modern fleets in Europe. The group has strategic relationships with carriers in counter-cyclical markets resulting in favourable winter leases, for part of the overall fleet, to three carriers in Canada and the United States. The fleet continues to be enhanced with the continued delivery of brand new 737-800s.
West Ham United Chairman Eggert Magnusson responded to the announcement of the partnership with the following statement: "West Ham United is delighted to announce XL.com as our new Principal Partner. They are an organisation very similar to ours in their values and aspirations for the future and a brand that we are proud to be associated with. We look forward to a long and successful partnership"
West Ham United's Deputy Chief Executive, Scott Duxbury, added: "This is the beginning of a brand new era at Upton Park and we are thrilled that XL.com will be an integral part of the club's future as we look to grow on and off the pitch. For some time now, we have been working hard to identify the right partner for West Ham United and, in XL.com, we have the perfect match."
Phil Wyatt of XL said: "The partnership between XL and West Ham United represents our desire to become one of the world's most well-known travel brands. The elevated status we will receive from being associated with West Ham United, with their proud history and being one of the most talked about clubs in the Premier League, is beneficial with regards to achieving our long-term goals."