Leo John Marentette Jr. (February 18, 1941 – May 8, 2014) was an American professional baseball player and relief pitcher in the Major Leagues who played for the Detroit Tigers (1965) and the Montréal Expos (1969).

Listed at 6 feet 2 inches (1.88 metres), 200 pounds (91 kilograms), Marentette batted and threw right-handed.

In a two-season career, Marentette posted a 4.32 ERA in five pitching appearances, giving up four runs on 10 hits and two walks while striking out one in 8+1⁄3 innings of work.

Then, in 1969, Marentette was recalled from Triple-A to pitch for the Expos during the expansion team's maiden season.

He appeared in three games during the Expos' June California road trip, one against each of the three teams based there, and gave up four earned runs in 5+1⁄3 innings.