The former France striker took the first step in enhancing his already-legendary status at the north London club, sidefooting home an angled finish in the 78th minute — 10 minutes after being introduced as a substitute.
Henry celebrated by running around the perimeter of the pitch past the delirious fans to hug manager Arsene Wenger, who brought the French striker back to the club for a two-month loan spell from New York Red Bulls.
"The feeling I had when I scored was amazing," the 34-year-old Henry told ESPN television. "I think I will always remember tonight."
The goal, which extended Henry's club-record tally to 227 goals, was a trademark finish, cutting in from the left to control an Alex Song through ball before curling the ball low into the far corner with his right foot.
Slapping his chest close to the Arsenal badge on his shirt, Henry acclaimed the rapturous cheers of the fans who voted him the club's greatest player in an online poll in 2008. The striker has been immortalized in a statue outside the Emirates Stadium thanks to his goalscoring exploits in his first stint with Arsenal from 1999-2007.
Prior to Henry's entrance, a weakened Arsenal had laboured against a Leeds team currently eighth in the second-tier League Championship and dogged by injuries.
Dominating possession, the hosts had little penetration up front with Marouane Chamakh struggling to make an impact in his last appearance before linking up with Morocco for the upcoming African Cup of Nations.
Andrey Arshavin and Aaron Ramsey fired shots over the bar in the first half before Mikel Arteta brought a smart save out of Leeds goalkeeper Andy Lonergan in the 54th.
It wasn't long before a frustrated crowd started singing Henry's name and Wenger soon obliged.
Henry had barely touched the ball before he ran inside his marker to meet Song's pass with the perfect finish, reviving memories Arsenal fans will hope he can keep on repeating until his return to the United States.