Hayes has recovered ahead of schedule from a hamstring injury picked up in the defeat to Inverness Caledonian Thistle on 15 February.
"He's been training the last few days. He's trained brilliantly as well," McInnes said.
"He looks ready to go and I'm delighted to have him back."
The Dons can move within one point of Premiership leaders Celtic with victory at Firhill, and McInnes knows a win is crucial in order to keep the pressure on Ronny Deila's faltering side.
"We're not daft, we all know the importance of winning and that's all we're looking for.
"I don't buy into all this psychological stuff, outside pressures and all the rest of it.
"For me it's just the game and we put enough demand on the players to win each and every game anyway. We want the players to play the way they train and hopefully we can be good enough on the night to win the game."
McInnes feels the form some of his players have displayed this season deserves consideration from Scotland manager Gordon Strachan.
With international friendlies against the Czech Republic and Denmark at the end of the month, McInnes believes two Aberdeen players in particular should be in the running for a call-up to the Scotland squad.
"I think there are a couple of lads there who have got a real case with their recent form. I know Mark Reynolds has been involved before, Peter Pawlett, Ryan Jack, but I think coming into that now are Kenny McLean and Graeme Shinnie.
"I hear others getting mentioned and pushed and quoted to be in the squad and I think everybody's maybe got a case for that but I look at those two certainly (for selection).
"Shinnie and McLean have been outstanding for me. They're in a team at the top end of the league, performed well in Europe and the improvement in them is clear."
Aberdeen manager Derek McInnes is "delighted" that Jonny Hayes has recovered from injury and is fit to face Partick Thistle on Tuesday.