[1][2][3] Competing at only seventeen in the 1930 Empire Games in Hamilton, Canada, he took the gold medal in the bantamweight class after winning the final against Tommy Holt of Scotland.

[4] In 1932 he was eliminated in the first round of the lightweight class at the Los Angeles Olympic Games, after losing his bout to the eventual bronze medalist Nathan Bor of the United States.

On 18 January 1934, he defeated Johnny Cuthbert in fifteen rounds at Kensington's Royal Albert Hall for the British Board of Control (BBofC) lightweight title.

[5] He successfully defended the BBoC British lightweight title only once, however, against Billy Quinlan on 4 August 1934 at Swansea, Wales, in a fifteen-round points decision.

[2] He lost the title on 29 October 1934 at the Royal Albert Hall in Kensington, London, to the vastly more experienced Jewish boxer Jack Kid Berg when his seconds threw in the towel at the end of the tenth of a scheduled fifteen round bout.

[6] Mizzler's defense was good, and he fought well at long range as was the English custom with a studied punch ready when needed, but he was no match against the relentless two handed attack of Berg who showed greater speed and dominated the infighting, throwing a vicious left to the jaw in the third that put Mizler to the ropes.

[2] On 19 October 1936, Mizzler attempted to take the British lightweight championship for a second time against Jimmy Walsh, but lost in a fifteen-round decision in Kensington.

As physical training instructor, he devoted his abilities to teaching thousands of airmen the rudiments of boxing until he had to leave the Air Force due to stomach ailments.