Keane, 29, collected his award at the club's annual dinner after taking his tally to 13 goals in 15 games during the 3-2 SPL win over Hibernian on Saturday.
The Republic of Ireland international joined Celtic on loan from Tottenham amid a display of public adulation hours before the transfer window closed at the start of February.
But his impressive personal form failed to prevent Celtic's season dipping further with Tony Mowbray sacked as their SPL charge faltered and Ross County inflicting one of the worst defeats in the club's history during the Scottish Cup semi-finals.
Keane also shared the top goalscorer award with Georgios Samaras, although both have netted one less than Scott McDonald, who was sold to Middlesbrough in January.
Keane's main award shows how few players have impressed consistently this season, although Aiden McGeady was a clear winner in the players' player of the year category.
Teenage defender Josh Thompson won the young player of the year prize while Paddy McCourt's solo strike against St Mirren in September was voted goal of the season.
John Kennedy, who was forced to retire from football in November because of his knee injury, won a special recognition award.
The awards night came hours after Rangers' 2-0 victory over Hearts extinguished any lingering hopes that Celtic caretaker manager Neil Lennon had of pipping their Old Firm rivals for the title.
Rangers need just one point to secure the silverware while Celtic could still face a challenge for second spot, which carries a place in the Champions League qualifiers.
Dundee United cut Celtic's lead to seven points with a 3-2 victory over Motherwell, which extends their unbeaten run to 11 games ahead of the visit of Lennon and his players to Tannadice on Sunday.
Celtic could go into the game with an even greater headache in central defence than normal after Darren O'Dea limped off against Hibs to leave Thompson playing alongside right-back Mark Wilson.
Lennon said: "He got a bad whack on his right ankle. Being the way he is, he wanted to carry on but it was impossible for him."
O'Dea had been playing through a thigh strain amid the absence of Glenn Loovens, Thomas Rogne and Jos Hooiveld.
Meanwhile, Celtic have told supporters to keep an eye on their official website for news on Wednesday's scheduled friendly against AZ Alkmaar.
Alkmaar, managed by former Rangers manager Dick Advocaat, are due to visit Celtic Park but the match is in doubt amid the continuing air embargo caused by the volcanic ash emanating from Iceland.