During the 1920s, Seddon played sparingly for the Arsenal first team, making his debut when deputising for Alf Baker in a 2–1 defeat against Sunderland on 10 April 1926. That was his only appearance of 1925–26, but edged his way into the first team with 17 appearances in 1926–27. However, he did not make the cut for the 1927 FA Cup Final, and with Arsenal's strong half-back line of Alf Baker, Jack Butler and Bob John. Seddon only played four times in 1927–28 and not at all in 1928–29.