Kozluk, 29 has signed for the Oakwell club after being released by Sheffield United after his contract expired last Saturday.
The former Poland U-21 international leaves Bramall Lane after eight years of service after he was signed in March 1999 by then manager Steve Bruce as part of a deal that brought Kozluk and Jonathan Hunt to Sheffield with Vassilis Borbokis heading to Pride Park.
During his eight year reign as right-back for the Blades he has scored just twice against Grimsby Town (2003) and Stoke City (2004), playing 215 games (+21) along the way.
Barnsley boss Simon Davey said; "We have pulled off a massive coup to bring Robert to Oakwell,"
"He did wonderfully well in the Premier League for Sheffield United last season and we are delighted to have him here."