The homegrown midfielder had been training with the Under-21s for the past two weeks after his latest off-field misdemeanour.
Grealish, 20, was demoted to Villa’s Under-21 side two weeks ago after he was pictured in the Daily Mail on a night out in Manchester following the club’s 4-0 defeat at Everton.
The Birmingham-born playmaker had been permitted to stay behind on Merseyside rather than travel back with the squad, but after his previous off-field misdemeanours, another headline-making incident prompted Garde to come down hard on him.
"[Grealish's actions] are not of the professional [standard] that I expect from my players”, the Frenchman told the likes of Sky Sports after reports of Grealish’s demotion emerged. “That's why Jack is training in the U21 team.
“He will not play with us, which is already a big punishment for a player. Now we will see the next step.”
However, Grealish is now back in the first-team fold, and after going the full 90 minutes in the Under-21s' 2-1 win over Derby County on Monday night, he could make his senior return in Sunday’s meeting with Arsenal at Villa Park.
"Jack is back with the group now,” Garde told avfc.co.uk. “I am pleased to have him back because he's an important player for the group.
"I am also pleased regarding how Jack trained over the past two weeks with the U21s.
"Jack is back. I am happy for that - and for the team."
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After bursting onto the Premier League scene during last season’s run-in, Grealish has endured a frustrating 2015-16 campaign so far, having struggled for form and fitness since picking up a hamstring strain at the start of Villa’s pre-season training camp in Portugal.
The former Republic of Ireland Under-21 international, who switched allegiances to England in September, has shown some flashes of his clear potential, but more often than not he has cut a frustrated figure amid the club’s worst-ever start to a top-flight term.
Speaking on his display in Monday night’s victory over Derby, Under-21 coach Gordon Cowans told AVTV: “Jack played in behind Libor [Kozak]. He’s a threat in that position if you can get him on the ball.
“But as you probably saw yourself, he should have got his shots off during the first half. At times, he’s going past people and you’re thinking, ‘Just hit it!’
“He delays it, but he’ll learn.”