Conor Hourihane's goal was his fourth of the season for Barnsley
Barnsley secured a first home league win since 27 August by inflicting Norwich's sixth defeat in seven games.
Tom Bradshaw put them ahead with a clever finish from Josh Scowen's cross and skipper Conor Hourihane fired home a superb second before the break.
Norwich were more assertive after the interval and Nelson Oliveira reduced the deficit with a low 25-yard shot.
The Canaries continued to press but Graham Dorrans and Jacob Murphy missed the target as Barnsley held out.
Norwich boss Alex Neil, who played more than 100 games for Barnsley during his playing career, made one change to the side that thrashed Brentford 5-0 last week, with Josh Murphy joining his twin brother in the starting line-up.
They were second best for most of the first half, though, as Bradshaw and Hourihane both scored their first goals since the home side's 4-0 win at Wolves in mid-September.
Neil, twice on the losing side for the Reds against Norwich in 2001-02, made a double change at the break as Josh Murphy and Alex Pritchard were replaced by Youssouf Mulumbu and Martin Olsson.
Oliveira's sixth of the season put them on the front foot, but their best effort in the closing stages was a shot from distance by full-back Ivo Pinto, which was saved by Adam Davies, as they slipped to eighth in the table, with Barnsley moving up to 11th.
Barnsley head coach Paul Heckingbottom: "It was a case of two teams playing two different shapes and I thought we imposed our shape on them better in the first half.
"They made changes at half-time and they imposed their shape and system on us at the start of the second half.
"It changes the mentality and we had to get to grips with the middle of the park again. They were much stronger with their midfield three so we had to change and regain control of the middle of the pitch.
"I don't think there's ever been a dip in confidence or belief. You need to not get down if things aren't going your way and don't get carried away if they are going your way."
Norwich boss Alex Neil: "We basically got bullied in the first half. Physically, we didn't compete.
"They're good at what they do and if you don't match it you're going to have a tough time. "To be fair to them, they thoroughly deserved the win based on their first-half performance.
"It wasn't down to tactics - we just didn't compete well enough, which is hard to accept. In the second half it was roles reversed and I thought we were totally dominant.
"You've got to be flexible in this league, take any test that comes your way and be good enough to overcome it."
