Hit-man Hearn played the last 15 minutes of the Stags 2-1 win at Rotherham United.
Hearn has not kicked a ball in anger since he suffered a cartilage injury in the Capital One Cup defeat at Sheffield United back in August.
Stags boss Adam Murray said: “Liam has made massive progress and is a couple of months ahead of schedule.
“It is great for Liam and great news for the club. He is strong and is now in a position to push on and build up his game time.
“Liam is gagging to play, but it does not change my mindset.
I will not put any time scale on him being back in the first team squad or put any pressure on him, this is his career at stake.” It had been feared that Hearn would be ruled out for the entire season following the latest injury setback to dog his recent career.
Mansfield fell behind, before Alex Fisher hit a brace to seal the win.