The St. Louis Cardinals picked him in the first-ever amateur draft, but McGinn chose to stay in school, getting his bachelor's degree in communication arts.

In 1966, the Cincinnati Reds took him in the first round (10th overall pick) of the secondary phase of the January draft, and he reported to Knoxville of the Double-A Southern League.

[1] On April 8, he would become the first relief pitcher in Expos history, as he came in for Mudcat Grant in the second inning in Montreal's first ever game, in Shea Stadium against the New York Mets.

[2] Six days later, on April 14, he earned the first MLB win in Canada with 51⁄3 innings of shutout relief as Montreal defeated the St. Louis Cardinals 8–7 at Jarry Park.

Altogether, McGinn appeared in a total of 210 games (28 starts) during his five MLB seasons, with 15 wins, 30 losses, 10 saves, and an earned run average of 5.11.