He signed with Giants at age 18 in 1950 and spent 51⁄2 seasons in their farm system before making his debut on June 3, 1955.

With Whitey Lockman shifting to left field, Harris became the Giants' starting first baseman for the rest of the season.

But he batted only .232 in 79 games played, and lost the 1956 starting job to future eight-time National League All-Star Bill White.

In 1957, the Giants' last season in New York City, White entered the military and opened up a spot for Harris as the team's backup first baseman.

On September 21, Harris hit the last homer by a New York Giants player, off Red Witt of the Pittsburgh Pirates at Forbes Field, part of a four-hit, seven-RBI day.

[1][2] He appeared as a pinch hitter in Giants' penultimate game at the Polo Grounds on September 28, fouling out in the eighth inning of a 1–0 defeat.