Lukaku converted Marcus Rashford’s pass on 33 minutes to bring Jose Mourinho’s side back into the game after Stuart Armstrong and Cedric Soares had put Southampton 2-0 ahead.
The goal ended a run of 12 games and 981 minutes without a goal for Manchester United in all competitions.
Ander Herrera would draw United level before half-time but neither side could find a winner after the break and had to settle for a point.
Lukaku’s last goal for United had come during the 2-1 victory against Watford at Vicarage Road on September 15.
The striker’s recent poor form is in sharp contrast to his debut season at Old Trafford following his £75 million ($95m) move from Everton.
981 - Romelu Lukaku's strike vs Southampton has ended a run of 12 games and 981 minutes without a goal for Manchester United in all competitions since netting against Watford in September. Relief. pic.twitter.com/xpoVjUoa1X— OptaJoe (@OptaJoe) December 1, 2018
Lukaku netted 27 times in all competitions last year, but Saturday’s strike at St Mary’s has taken his tally this campaign to just five.
His struggles in front of goal have not crossed over to the national team, where he has scored five goals in his last four appearances for Belgium.
Manchester United boss Jose Mourinho revealed he met with Belgium boss Roberto Martinez during the international break in an attempt to better understand the striker’s contrasting form.
Lukaku came off the bench in all three matches, but failed to find the back of the net in any of them.
Despite his anger, Lukaku insists he still has a good relationship with Mourinho and would “run through a brick wall” for the former Chelsea and Inter Milan manager. He also says he intends to stay at Old Trafford for as long as United want him.
Lukaku played 86 minutes for United on the south coast before being replaced by Jesse Lingard.
The draw lifted United back above Leicester into seventh place but they remain six points adrift of the top four and a huge 16 points behind leaders Manchester City.
Next up for United is a match against Arsenal at Old Trafford in the Premier League on Wednesday.