The 28-year-old was the Tykes Players' Player of the Year in the 2011/12 season after an impressive campaign in which he made 46 appearances.
But McNulty struggled with injury last season, playing just 14 matches, to leave him itching to make amends in 2013/14.
"I'm delighted to have signed and can't wait to get back and get started again. It was an unbelievable end to the season and we'll hopefully kick on for a good start to the new one," he told the club's official website.
"In my first season here I played 46 games and won Players' Player of the Year, it was a great season for me. I really asserted myself on the team, but then last season only made 14 or 15 appearance so I really want to do well again and keep fit.
"I am a team player and I like to think I play my part in the dressing room. Whether I'm playing, on the bench or sat in the stand I'm behind the team.
"I got fit and raring to go at the end of the season, but the big picture was that we stayed up and that was incredible. I'm ready now to get straight into it. It's exciting to look ahead.
"I think everyone is galvanised from our experiences at the end of the season. Flickers' (manager David Flitcroft) part in it was monumental in turning our fortunes around. He sparked everyone into playing 50 percent better than we had done and I hope everyone can ride that wave of euphoria into the start of a new season.
"With our new bond under the new management team the players just seem to want to run through walls for the manager. I've never really known it before, but I've felt the change.
"If I keep fit I know I'll be alright, I know I'm a good enough player to play in this division. I want to play every week.
"In terms of Barnsley I'd be disappointed if we weren't comfortably in mid-table next season."