His family moved to Oroville, California when he was young and he graduated in 1966 from Oroville High School. In February 1965 at age 17 he married high school sweetheart Carole Widener. They eventually had four children, Gary Jr., Tim, Mark and Kathy.
In 1970 Nolan went 18–7 with 181 strikeouts and a 3.26 ERA, helping the Reds to win the NL pennant and establishing himself as one of the league's great young starting pitchers. Nolan pitched a remarkable nine innings of shutout ball to earn a victory in the 10-inning Game One of that year's National League Championship Series against Pittsburgh. But he took the loss in Game One of the World Series against the eventual champion Baltimore Orioles.
After a disappointing 12–15 record in 1971, he posted 13 victories before the 1972 All-Star Game. Selected for the NL team, Nolan was suffering from neck and shoulder pains, and he was forced to withdraw from the game. After rehabbing his injuries on the disabled list, he returned to the lineup and finished the season with a 15–5 record and 1.99 ERA, leading the league in winning percentage (.750) and was second to Steve Carlton in ERA. In the World Series against Oakland that year, he lost Game One (six innings, three runs) and was pulled from the game early in Game Six (41⁄3 innings, one earned run).
Arm problems forced Nolan to miss most of 1973, and he missed the entire 1974 season. He returned in 1975 in good form, going 15–9 with a 3.16 ERA. In the World Series against Boston, he pitched just six innings in two starts. In 1976, he duplicated his 15–9 record and finally got his first World Series victory against the Yankees in the last game of a four-game sweep. New arm and shoulder problems bothered him in 1977, and he opted to retire.
In 10-season career, Nolan compiled a 110–70 record with 1,039 strikeouts, a 3.08 ERA, 45 complete games, 14 shutouts, and 1,674 innings pitched in 250 games (247 starts). In eleven post season games he was 2–2 with a 3.34 ERA covering 59.1 innings.
He moved back to Oroville in 2003, where he is involved with several charitable and civic organizations and works with high school pitchers. In 2011 he was inducted into the Oroville Union High School District Hall of Fame.