Arsenal's record goalscorer had rejoined the club he left for Barcelona in 2007 on a short-term loan deal from New York Red Bulls and did not disappoint when he slotted home on 78 minutes to finally break the resistance of the npower Championship club.
Henry, 34, is available for a six-week spell which will take in matches against Manchester United, AC Milan in the Champions League and possibly even the showdown with arch-rivals Tottenham on February 26.
And given tonight's 20-minute cameo masterclass, that could just be the spark Arsenal need to push on towards a successful end to a season which started so badly.
The Gunners, who rested current captain Robin van Persie, started strongly.
Andrey Arshavin was set up by Marouane Chamakh, who was set to leave for the African Nations Cup with Morocco after tonight's game, but the Russian blasted over from edge of box.
Arsenal pressed for long spells as Leeds were pushed deeper and deeper, but they lacked any real spark in the final third.
Sebastien Squillaci headed wide at the far post when Mikel Arteta, captain for the evening, whipped over a free-kick from the right.
At least on-loan Tottenham winger Andros Townsend was showing some endeavour for the visitors as he made some progress down the left flank, but he lacked support in the middle.
On 15 minutes, Aaron Ramsey bolted to the edge of the Leeds penalty area and drove a rising shot just over the angle.
The Wales captain then saw his 12-yard effort deflected over following another mazy run by Arshavin.
Leeds were shouting for handball when Luciano Becchio's shot came off Laurent Koscielny, but replays showed the ball hit the defender's back rather than arm.
There was some concern for Arsenal - already stretched in defence by a string of injuries - when Francis Coquelin pulled up clutching the top of his hamstring.
Nico Yennaris, an 18-year-old England youth international, came on after 33 minutes to fill in at right-back.
The start of the second half brought more of the same as Arsenal probed the Leeds defence without making any real progress around the edge of the area.
When Arshavin was picked out in space on the right by a lovely cross-field pass by Ignasi Miquel, the Russian's attempted half-volley flew horribly wide.
Arsenal then worked the ball well down the left, with Alex Oxlade-Chamberlain cutting back to Chamakh, whose lay-off picked out Arteta, but goalkeeper Andy Lonergan made a fine one-handed save.
Oxlade-Chamberlain stung Lonergan's hands with a fierce drive as Arsenal remained camped in the Leeds half.
With 22 minutes left, Wenger signalled for his talisman as both Henry and Theo Walcott were introduced, replacing Chamakh and Oxlade-Chamberlain.
The French World Cup winner wiped away a tear as he ran out to rapturous applause, with his first touch coming as he drifted offside.
However, his next intervention completed the fairytale comeback on 78 minutes as he collected Alex Song's pass into the left-hand side of the area before dispatching a trademark finish inside the far post to send the Emirates Stadium into a frenzy.
It was an historic moment indeed as the whole Arsenal team ran to celebrate Henry's 227th goal for the club, as he headed for the bench to embrace Wenger.
There was still life left in the tie as Leeds substitute Ross McCormack headed straight at Wojciech Szczesny.
Arshavin drilled another good chance into the side netting before Szczesny made a good reaction save at the other end to keep out a near-post shot from substitute Mikael Forssell.
The night, though, was always only ever about one man and Henry stood arms aloft at the final whistle, basking in glory of his own making once more.