The name Robert McDonald first became known in hockey circles back in 1941 when the high-scoring winger netted 23 goals and 37 points in just 18 games for the St. James Canadians of the MJHL. He was limited to just two games with the Detroit Mansfields of the MOHA in 1941-42 with much of the country's focus on World War Two. The following year he dressed for eleven games with the Windsor Army hockey squad.
The NHL was ravaged by defections due to the War, and it left teams actively seeking out replacements for those who were called to serve active duty. An opportunity arose for McDonald to play in the NHL with the New York Rangers in 1943-44 and he jumped at the chance. It was just a one-game call-up, but it was by far the most memorable game of his career. Although he was held off the scoreboard, it was a chance to play with and against some of the best hockey players in the world. He played two years in New York with the Rovers of the EAHL and once said it was thanks to hockey that he got to see such other incredible cities as New York.
In the fall of 1945, and the return of most of the NHL regulars following the conclusion of the War, McDonald returned to Ontario and signed with the IHL's Windsor franchise. He played the final three years of his career with Detroit, retiring in 1949 at the age of 26.