A right-hander, Humphreys was a relief pitcher over all or parts of nine Major League Baseball seasons (1962–1970) with the Detroit Tigers, St. Louis Cardinals, Chicago Cubs, Washington Senators and Milwaukee Brewers.

After trials with Detroit (1962) and St. Louis (1963), Humphreys was recalled from the Triple-A Jacksonville Suns in July 1964, and worked in 28 games out of the Redbird bullpen.

He won his only two decisions (both coming during the September pennant race) and posted two saves with a 2.53 earned run average as St. Louis overcame the Philadelphia Phillies to win the National League championship.

In Game 6 of the 1964 World Series, he worked the ninth inning and retired the New York Yankees in order;[1] it was Humphreys' only post-season appearance.

After his playing career ended, Humphreys remained in baseball as a player development director and minor league field coordinator for the Brewers, Cardinals and Toronto Blue Jays.