The Portugal international was suspended as a precaution by the Ligue de Football Professionnel (LFP) back on February 6 following an incident in a game away at Nimes five days earlier.
Martins pushed Mikael Lesage twice during his side's 3-1 Ligue 1 defeat, initially making contact with the official following team-mate Tiemoue Bakayoko's 32nd-minute red card.
The winger, who joined Monaco permanently from Atletico Madrid in 2019, was sent off and reacted by shoving Lesage for a second time.
After examining footage and speaking to Martins, the LFP has punished the player with a lengthy ban that is backdated to the time he was initially suspended.
The 24-year-old has already sat out five games but will now miss the remainder of the domestic season in France.
Monaco issued a short statement in response to the verdict, describing the punishment handed down as a "very heavy sanction".
"AS Monaco takes note of the decision of the disciplinary committee of the LFP to sanction Gelson Martins with a firm suspension of six months dating to February 6, a very heavy sanction," the club said.
"The club once again condemns the unjustifiable behaviour of its attacker, but also regrets the excessive length of this suspension for a player who has never known a disciplinary ban in more than 200 games at the highest level."