QPR remain rooted to the bottom despite coming from behind to lead 2-1 through goals by their Kiwi captain Ryan Nelsen and substitute Djibril Cisse but McCarthy's second consigned them to their third successive draw since Redknapp replaced the sacked Mark Hughes.
The draw also saw QPR set a new unwanted Premier League record of 16 games without a win from the start of the season. The last top-flight team to suffer a 16-game winless start to a season was Sheffield United in 1990 in the old First Division.
It leaves QPR on just seven points, eight points adrift of fourth from bottom Wigan.
The hosts had started the brighter, David Jones being desperately unlucky not to open the scoring with a terrific freekick but set the record straight soon after as McCarthy rattled the ball home with an excellent volley.
The visitors, though, were level seven minutes later as Nelsen headed in at the back post with his first goal for the club he joined from Blackburn Rovers.
Nelsen, though, almost handed Wigan a second goal as his error let in McCarthy but former England goalkeeper Robert Green did well to deny the Irishman with his legs.
However, the hosts had the upperhand and pinned the London side back in their half, Green doing well again to deny Jordi Gomez from close range.
Jones then went close to restoring Wigan's lead but Green stood up to him well, though, he could do nothing about a piledriver from Gomez that hit the underside of the bar but failed to cross the line.
However, totally against the run of play QPR grabbed the lead as Cisse nipped in to take advantage of a defensive error by Adria Lopez and slot the ball past Ali Al Habsi.
Seconds later the hosts were back on level terms as Chilean Jean Beausejour put in a great cross which found McCarthy, who put the ball away.
Green came to QPR's aid again as the game drew to a close getting down well to save from Gomez.