[3][4][5] Dai Prosser was born in Neath, Wales, he was a Bombardier in the British Army during World War II,[6] and he died aged 60 in York, Yorkshire.

[7] Dai Prosser played at prop in Leeds' 19–2 victory over Halifax in the 1940–41 Challenge Cup Final during the 1940–41 season at Odsal Stadium, Bradford, in front of a crowd of 28,500, played at prop in the 15–10 victory over Halifax in the 1941–42 Challenge Cup Final during the 1941–42 season at Odsal Stadium, Bradford, in front of a crowd of 15,250, he missed the 15-16 aggregate defeat by Dewsbury in the two-legged 1942–43 Challenge Cup Final during the 1942–43 season at Crown Flatt, Dewsbury and Headingley, Leeds, and played at prop in the 8–4 defeat by Bradford Northern in the 1947 Challenge Cup Final during the 1946–47 season at Wembley Stadium, London on Saturday 3 May 1947, in front of a crowd of 77,605.

[7] During Dai Prosser's time at Leeds, they appeared in four Challenge Cup Finals winning two (1941 and 1942), and losing two (1943 and 1947), he appeared in three of these Challenge Cup Finals, and was on the winning side twice.

Dai Prosser played at prop in York's 9–2 victory over Wakefield Trinity in the 1936 Yorkshire Cup Final during the 1936–37 season at Headingley, Leeds on Saturday 17 October 1936, and played at prop in Leeds' 14–8 victory over Huddersfield in the 1937–38 Yorkshire Cup Final during the 1937–38 season at Belle Vue, Wakefield on Saturday 30 October 1937.

Dai Prosser was the assistant-coach to Joe Warham in Leeds' 25–10 victory over Warrington in the Championship Final during the 1960–61 season at Odsal Stadium, Bradford on Saturday 20 May 1961, in front of a crowd of 52,177.