[13] Union High School's theatre department, under the direction of James Mosser, produces two major theatrical productions annually and has been recognized numerous times by the Paper Mill Playhouse in their annual Rising Star Awards.

[15] The Union High School Marching Band consists of wind, percussion, and color guard members.

At the 2012 Yamaha Cup, with their show entitled, "Rosie", the marching band won 1st place in Group 4A competition and received the awards for Best Music, Best Visual, and Best Overall Effect.

In 2014 with their show entitled, "Soaring", the marching band won 1st place in the USBANDS Group 3A New Jersey state championship at Rutgers University and received the award for Best Overall Effect.

[19] The football team competes in Division 5A of the Big Central Football Conference, which includes 60 public and private high schools in Hunterdon, Middlesex, Somerset, Union and Warren counties, which are broken down into 10 divisions by size and location.

[30] In the 1979 North II Group IV final, the team won the championship with a 35-24 victory against a Livingston High School team led by quarterback Stan Yagiello at Giants Stadium in front of 15,000 fans [31] The 1991 team came back from a 14-0 at the half to defeat Randolph High School by a score of 24-14 in the North II Group IV championship game, to end Randolph's 59-game unbeaten streak, which was the longest at the time in state history.

[32] The 1992 team, ranked fifth in the nation by USA Today, finished the season with an 11-0 record and extended their winning streak to 22 games after taking the North Group IV state sectional title with a 21-7 victory against Randolph High School in the championship game played in front of 7,000 fans.

[33][34][35] In 1993, the team beat Randolph 19-6 to win the North II Group IV sectional championship and finish the season 10-1.

[36] In 2019, the team won the North II Group V sectional title, the program's first in more than a quarter century, with a 42–28 win against Clifton High School in the championship game.

[38] The softball team won the Group IV state title in 1989, defeating Middletown High School North by a score of 3-1 in the championship game.

The boys' basketball team won the Group IV state championship in 1997, coming back from being down 10 points in the fourth quarter to defeat Atlantic City High School by a score of 61-50 in the tournament final played at Boardwalk Hall.