Pitching in relief of starter Ray Washburn, Gullett debuted on April 10, 1970, on the road against the San Francisco Giants.

[5] In his rookie season, Gullett appeared in 44 games (42 in relief) posting a 5–2 record and a 2.43 earned run average.

[7] Gullett was the pitcher when Willie Mays hit the 660th and last home run of his Major League Baseball career on August 17, 1973.

[9] He went 6–1 with a 1.83 ERA and 42 strikeouts in 54 innings pitched in July 1974, winning the National League Player of the Month Award.

As noted in the Gullett's biography in the Society for American Baseball Research (SABR): "The three best southpaws of the previous generation—Warren Spahn, Whitey Ford, and Sandy Koufax—were in the Hall of Fame.

"[12] Following the 1976 season, Gullett became a free agent and signed with the New York Yankees, the month after his Reds had swept them in the World Series.

During the fourth inning, Gullett slipped and fell on the wet pitching mound, spraining his ankle and straining a muscle in his neck.

Shoulder surgery to repair a double tear of his rotator cuff in 1978 signaled the end of Gullett's career at age 27.

[16] During a nine-year career, Gullett accumulated 109 wins and posted a 3.11 earned run average and tallied 921 strikeouts.

The farmland's caretaker was his brother Jack, who was indicted on a charge of trafficking in a controlled substance the following month on September 30.

[27][28] Gullett died on February 14, 2024, at OhioHealth Riverside Methodist Hospital in Columbus, Ohio, due to heart issues and other natural causes at the age of 73.