St Johnstone moved up to eighth in the Scottish Premiership as the visitors suffered only their second league defeat of the season.
May opened the scoring before providing an assist for Dave Mackay who doubled the home side's advantage in the first half. May then provided a further two second-half assists for Steven Maclean as St Johnstone recorded their third win of the season.
The away side were never really in the contest and the home side registered the first shot on target when Gary McDonald's close-range effort was saved by Inverness goalkeeper Dean Brill after 13 minutes.
They didn't have to wait long to break the deadlock with McDonald heavily involved in the goal after 17 minutes.
His cross was met by May who steadied himself before drilling home a powerful shot from the right side of the six-yard box to claim his seventh goal of the season.
St Johnstone continued to dominate proceedings and May will have been disappointed not to extend the home side's lead after missing two further chances.
But the home side were rewarded after 26 minutes when Mackay gave them a two-goal cushion after receiving a pass from May before smashing home an unstoppable left-footed shot from outside the area.
The home side almost extended their lead five minutes later but McDonald's shot from an acute angle was saved by Brill.
It was all St Johnstone and they rounded off the half with a long-range effort from David Wotherspoon that was comfortably gathered by Brill.
The home side began the second half as they ended the first with Nigel Hasselbaink forcing Brill to claw away an effort which looked destined for the top corner.
May then forced another save from Brill before helping his side get the third goal their play deserved.
He passed to Steven Maclean who hit a rasping shot from outside the box into the bottom left corner of the net.
May was denied by Brill on 80 minutes, but just a minute later, he crossed for Maclean who capped a memorable day for St Johnstone by slotting home from point-blank range giving the home side all three points.