Reardon played college baseball for the University of Massachusetts Amherst. While at UMass, he played collegiate summer baseball for three years (1974-76) with the Cotuit Kettleers of the Cape Cod Baseball League, and in 2000 was named a member of the inaugural class of the Cape Cod Baseball League Hall of Fame. After college, Reardon went undrafted and signed a minor league contract with the New York Mets in 1977, and was assigned to the Lynchburg Mets in the Single-A Carolina League. Although undrafted, Reardon quickly made his way through the Mets' farm system, compiling a 30–9 record with a 2.68 ERA and 6 saves in 74 games combined between Lynchburg, Jackson in 1978, and Tidewater in 1979.