The Potters' long-throw specialist has struggled for fitness and form this season and has now signed for the Championship outfit until the end of the season
The veteran, best known for his powerful long throws, has been hampered by injury so far this term and has struggled to earn playing time as a result.
And he has admitted he will find it difficult to temporarily leave the club he joined in 2006 despite his desire for first-team football.
"It's a big wrench to be heading out because I love the club and I have had some wonderful times here over the past six-and-a-half years," he told the club's official website.
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"I'm quite happy that a Championship side have come in for me. They're in a relegation battle, but they've put together a little run of late to raise hopes that they can climb out of trouble, so I’m looking forward to the challenge."
Potters boss Tony Pulis was full of praise for Delap, who has played for the likes of Derby County, Southampton and Sunderland over the course of his career.
"Rory has been a bedrock of the progress this Club has made since he joined us," he said.
"It's important therefore that we look after those players who have served us so well and helped us to get where we are today.
"One way or another, it’s been a frustrating time for him this season, but we are delighted that he’s now got the chance to go out and play regular first team football. I am sure that he will prove to be a great acquisition for Barnsley."