The former Trinidad and Tobago striker has agreed terms on a six-month contract and will go straight into David Flitcroft's squad for Tuesday's clash with Millwall at Oakwell.
The 33-year-old had his contract with Ipswich terminated by mutual consent after he was restricted to just one first-team appearance since the appointment of Mick McCarthy as manager in November.
Scotland scored 45 goals in only 90 matches for Swansea before joining Wigan, where he found the net only once in 32 games.
He added 19 goals after joining Ipswich in 2010, and he is now determined to prove he is worthy of a first-team place at Barnsley.
"I'm looking forward to getting back to playing football," Scotland said. "Everyone is really positive here. I'm going to try and bring more goals to this team."