Broadhurst, 50, began the last round four shots adrift of overnight leader Miguel Angel Jimenez, but a final-round 68 was enough to clinch him his first major title as the Spaniard fell away to card a three-over-par 75.
Broadhurst, who shot 75 on the opening day, finished on 11 under par, two shots ahead of American Scott McCarron, who closed with a 69, while Jimenez finished a shot further back and tied for third with Sweden’s Magnus Persson Atlevi.
Atlevi closed with a 67 to join Jimenez on eight under, ahead of four Americans. Brandt Jobe and Tom Byrum both finished seven under ahead of Joe Durant and Wes Short Jr (both six under).
Bernhard Langer, who won the Senior Open at Carnoustie in 2010, shot four consecutive rounds of 71 to finish on four CARunder, seven shots back.
Broadhurst is the first player to win the Senior Open on their debut since Fred Couples in 2012 at Turnberry and is the first English winner on the European Senior Tour this year.