The Wales international was back at Albion for the first time since being sold by the club for £3million in January.
Predictably he popped up with the winning goal - his 11th of an impressive season - as Norwich picked up only their second away win of the campaign.
It must be something about the air in the West Midlands that inspires Norwich as their other win on the road came at Birmingham City.
Their fourth win in six games since the arrival of new manager Peter Grant did have some degree of fortune to it as out-of-luck Albion amazingly hit the woodwork six times.
But Norwich rode their luck successfully and Earnshaw stunned Albion in the 57th minute when he headed home Jurgen Colin's cross.
It just deepened the misery for Albion who have lost their way since the appointment of new manager Tony Mowbray.
The latest setback means Albion have picked up just one point from their last four games - hardly the form required for a team hoping to make an instant return to the Premiership.
Albion could have been well in control of affairs of by half-time only to be frustrated three times in the space of just two minutes by the woodwork.
It took them 30 minutes to get into gear and before then they were fortunate not to find themselves trailing.
Norwich were unlucky not to break the deadlock after just 10 minutes when Adam Drury's far post cross was met by Andy Hughes whose header was tipped over by Russell Hoult.
With the potent Darren Huckerby causing major problems for Albion, it seemed only a matter of time before one of his crosses would be converted.
But Norwich were unable to capitalise on Huckerby's good play and Albion worked their way into the game - only to be left cursing the woodwork.
Steve Watson hit the post when well-placed in the 36th minute before the normally reliable Kevin Phillips crashed his close-range shot off the post a minute later.
Jason Koumas then became the third Albion player to be denied by the woodwork when his 25-yard drive crashed off the bar.
Earnshaw made them pay before Albion's dismal day was summed up when skipper Curtis Davies crashed his header off the post and Koumas and Jonathan Greening were both denied by the bar.