Seymour made his first-class cricket debut for London County Cricket Club in 1900 but played only three times for the side and was offered a place in Kent's Tonbridge Nursery where young professionals were coached by Captain William McCanlis. He first appeared for Kent in 1902 having qualified for the County by residence, and was soon a regular in the side, appearing at least 20 times each season until World War I and in all but two seasons until his retirement at the end of the 1926 season. A right-handed batsman, he was part of the Kent side which won the County Championship four times between 1906 and 1913.