He spent all or parts of seven seasons (1960–66) in Major League Baseball as a member of the Cincinnati Reds, Baltimore Orioles and Houston Colt .45s/Astros.

[1] After receiving brief trails with the 1960 and 1961 Reds, he made the team's 25-man roster in 1962, batting .231 in 60 games played as a reserve outfielder, then was traded to Baltimore that December.

In 1963, Gaines occasionally spelled left-handed-hitting Boog Powell as the Orioles' left fielder and batted an MLB career-high .286.

The 1965 season saw Gaines lose his regular job to Rusty Staub and he reverted to a backup role; although he appeared in 100 games, he batted only .227.

Apart from a brief stint with 1966 Astros, when he garnered only one hit in 13 at bats, Gaines spent the final three seasons of his playing career in the Triple-A Pacific Coast League.