After studying landscaping in England, Jack met famed golf course architect Alister MacKenzie in 1919 and worked with MacKenzie's group until the architect's death in 1934. During this period, Jack Fleming served as timekeeper, paymaster and construction foreman at various projects throughout England, Scotland, France and Ireland.
In 1926, Jack Fleming was sent to California to supervise construction of the Meadow Club in Fairfax. Although he came to America on a two-year visa, it would be 40 years before the senior Fleming would return to Ireland. During his stay in the United States, he worked closely with MacKenzie associate Robert Hunter in constructing such famous California courses as Cypress Point Club in Pebble Beach, the Valley Club of Montecito in Santa Barbara, Green Hills Country Club in Millbrae, Sharp Park Golf Course in Pacifica and Pasatiempo Golf Club in Santa Cruz.
After helping with the finishing touches on the Sharp Park course in 1932, Jack Fleming accepted a position with the City of San Francisco Parks and Recreation Department, maintaining the city's courses. But buoyed by the knowledge he gained from working with MacKenzie and Hunter, he continued to work in golf course design and construction throughout California.