The new recruit, who joined from Coventry on Friday, made his Reds debut 24 hours later and was involved in two of the goals in a 3-2 win at Bundesliga 2 side Arminia Bielefeld.
There was another goal for Cauley Woodrow, his seventh of pre-season, while Luke Thomas bagged two.
Chaplin's debut, even if it was in a friendly, will be proof to Barnsley that patience is a virtue after they finally got their man.
He had been a target for the entire summer as well as previous interest in January and last summer.
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“I'm glad it's over the line now," Chaplin said.
“There's been a bit of speculation over the summer, but I'm glad to finally be here and now I'm just raring to get going.
“It was close to happening last year, but I don't know what happened and I ended up at Coventry. But Barnsley had a great season, it didn't happen for whatever reason but here I am now and I'm delighted.”
Despite arriving so late into pre-season, with just one game left before the Reds kick-off their Championship campaign against Fulham on August 3, Chaplin is not concerned.
"I think I can fit in seamlessly. The gaffer (Daniel Stendel) here likes to attack, to play football the right way and expects his side to press high up the pitch.
"That's the modern game now, it's about fitness and working hard without the ball, behind the ball. And that's something I'm looking forward to being a part of.”