Born in Johannesburg in 1916, Dudley came to the UK as a young man to try his luck as a footballer. He had trials at Dundee and a year at Clyde before joining Chesterfield in November 1938. Dud made his debut against Sheffield United on November 12th., 1938, playing against the notoriously hard Tommy Johnson. Spireite legend has it that, after their opening few clashes, Johnson had had enough, and kept his distance for the rest of the game: this was reckoned to be the only such time that Johnson had been so intimidated in his long career.

Milligan was an enigma. He was reckoned to be likeable and soft-spoken off the pitch, although Hugh McJarrow, who often drew the short straw to "room" with Dud on away trips in their one season together, apparently had the bruises to suggest that Millingan in "playful" mode wasn't much different  than in a match! Once he crossed that white line, he became volcanic, and little had to happen to make him erupt. Physically, he was immensely strong, and anyone who threw down the gauntlet invariably came off worse. As often as not, Milligan started it and was sent off many times in his career, suffering long periods of suspension, particularly during the ad-hoc games of the Second World War.

After two years of wartime football, he made for Belfast, working as a welder and playing for Linfield, Larne and Distillery. Having been capped three times for South Africa, he made one appearance for Ireland against Wales in 1939, becoming the only Chesterfield player to score at full international level.

After the war ended he returned to England and picked up with Chesterfield, but he was allowed to join Bournemouth in the summer of 1947. A year or so later he joined Walsall, seeing out the end of his pro career with the Saddlers.