Devlin attended Georgetown University in Washington, D.C., where he played baseball and football. As a senior in 1900, he served as the team captain. He was a standout back, and in 1900 was considered competitive for the Walter Camp All-American team if it had not been restricted to Harvard, Yale, and Princeton players.
He served as the head football coach at North Carolina A&M, now North Carolina State, for the 1902 and 1903 seasons. During that time, Devlin's teams compiled a 7–8–2 record for a winning percentage of .471.
Devlin spent most of his nine-year baseball career with the New York Giants, where he started as their third baseman in 1904. In 1905 Devlin stole 59 bases, sharing the National League lead with Billy Maloney of the Chicago Cubs. Devlin was traded to the Boston Braves in 1911, where he played for two years as a backup infielder until his retirement in 1913. Devlin had a short temper and on one occasion in 1910, jumped into the grandstand at the Polo Grounds to beat up a fan who called him a "dog".