The Paisley side have lost just once in their last nine games as they have closed to within five points of a coveted berth in the table's top half.
McGowan, who had been out for three months after going under the knife, has increasingly sparkled for Danny Lennon's men.
Now Fitzy believes that the ex-Celtic player can propel his former side into the top-six stratosphere and also play a key part in masterminding a Scottish Communities League Cup semi-final shock against his old team.
The Saints legend said: "I think the return of Paul McGowan from injury is massively important to St Mirren.
"He is the catalyst to so much that is good in the team and in that free role that he has, teams just don't know how to pick him up.
"Not only does he create so much for St Mirren, he also draws players to him and that leaves space for others to operate in.
"To have been without him for three months was a massive blow for the club and I don't think there is much of a coincidence that his absence corresponded with the poor run that we went on.
"But the great thing is that the side have shown a lot of character to come out of that period and they did so even before Paul got back from injury – now his return has given them an extra lift.
"In many ways with the team starting to play so well it is a frustration that we are now going into the break but that is the way it goes.
"The main thing is that the belief is right back in the side and we are back to just five points off a top-six place and have a League Cup semi-final to look forward to.
"I have no doubt that with McGowan back in the side we have a far better chance of success in both of these than without him."
While Saints' dismal record against Celtic has been well documented, the Buddies' Scottish Cup-winning legend reckons that it can be different when the two sides get it on at Hampden at the end of the month.
Fitzy said: "I think the wide open spaces of Hampden will really suit St Mirren. On top of that, they will be going into that one as massive underdogs given their record against Celtic. That will suit us.
"Looking back at Celtic's results in both cup competitions last season, they lost the League Cup final to Kilmarnock and the Scottish Cup semi-final to Hearts at Hampden and we definitely have a chance.
"But the main thing going into any big cup game is belief and the side certainly have that back about them.
"So if we are ever going to get the better of Celtic then this could be the game."
Fitzpatrick also took time to praise the passing ethos of Buddies boss Lennon and labelled the current St Mirren side as the most attractive footballing side since his own Scottish Cup-winning team of the late Eighties.
He said: "I am a regular at St Mirren Park and the one thing you can guarantee is that you are not going to leave the new stadium without being entertained.
"There is no doubt in my mind that the current St Mirren side play a brand of football that is the best I have seen since our cup-winning side and the current bunch are a damn sight fitter with it!
"I am very hopeful that this season could be one to remember and that would be a great reward for what Danny has achieved with St Mirren."