Cummings was born in 1927, in Adelaide, South Australia, the son of the accomplished Irish-born trainer Jim Cummings, who trained the great stayer Comic Court to a win in the 1950 Melbourne Cup. Bart started his career working for his father as a strapper, despite being allergic to horses and hay. Cummings had an older brother, Pat, and said of his father; "I had the best of teachers. My dad had a lot of experience behind him and I picked up from him by watching, listening, and keeping my mouth shut".