The partnership between the brewery and The Boat Race Company extends for the next six years.
Andy Wood, chief executive of Adnams, said: "Adnams is delighted to become the official beer partner of The BNY Mellon Boat Races.
“The races are a firm favourite on the calendar and in many ways signifies the first big day out in London after the winter.
“We look forward to working with The Boat Race Company for the next few years and am proud to associate Adnams with this national and internationally famous event."
David Searle, executive director of The Boat Race Company, said: "It is a pleasure to announce Adnams Southwold as official beer partner of The BNY Mellon Boat Races.
"I look forward to working with them, and it is exciting to think of how much we will achieve over the next six years.”
The first boat race between Oxford and Cambridge took place in 1829. However, the event did not become annual until 1856.
Its official name became the BNY Mellon Boat Race when BNY Mellon began sponsoring the event in 2013.
The BNY Mellon Boat Races will next take place on Sunday March 27, 2016.
The Newton Women's Boat Race will begin at 3.10pm, with The BNY Mellon Boat Race following at 4.10pm.