Keily did not take an interest in competitive running until he was 28, after one of his brothers joined the Derby and County Athletic Club. In 1949 Arthur joined the club as well (as did, eventually, all six of his male siblings), but did not participate in his first marathon until 1953, finishing 12th in an event that spanned from
Doncaster to
Sheffield. One year later, however, it was in this race that he recorded his first victory, completing the course in 2:30:45, five seconds ahead of the previous year's champion. Between his first victory and his appearance at the
1960 Summer Olympics, he competed in twenty-seven local and international marathons, winning eleven of them and placing within the top three in an additional six. After failing to qualify for the
1956 Summer Olympics, Keily participated in the
Košice Marathon twice, finishing 12th in 1956 and 6th in 1957, and then attended the
1958 British Empire and Commonwealth Games as a representative for the
England athletics team, completing the
marathon in 12th position after falling ill shortly before the race. He blamed his performance on the team's arrival too late to acclimate to Rome's conditions. During this period Keily also participated in twenty-one British national road relays, helping set new records in thirteen of them, but he retired from active competition following his sole Olympic appearance. He had set nine world records during his career: the half marathon, the track marathon, 15, 30, and 45 miles, 45, 50, and 60 km, and the furthest distance run in three hours. (#58),
Bakir Benaïssa, Keily (#46),
Aurèle Vandendriessche (#36), and
Rhadi Ben Abdesselam (#185).|300px|alt=Arthur Keily competing at the 1960 Summer Olympics, near the 10-kilometre mark ==Later life==