He appeared in 533 games over all or part of seven seasons in Major League Baseball for the Baltimore Orioles (1959, 1963, and 1968) and Washington Senators (1964–1968).

Valentine was a switch hitter who threw right-handed; he was listed as 6 feet 1 inch (1.85 m) tall and 190 pounds (86 kg).

In 1964, Valentine finally spent extended time on a big-league roster, getting into 102 games and substituting in all three outfield positions.

His acquisition by the Orioles was insurance in case Paul Blair was ordered to report for active duty with the United States Army.

On the cusp of winning three straight American League pennants (1969–1971), Baltimore outrighted Valentine to Triple-A Rochester for 1969.

All told, Valentine batted .247 in major league action, collecting 360 hits, with 56 career doubles, ten triples and 36 homers.