The 24-year-old graduate of Manchester United's academy was released in June after three years with the Eagles.
Fryers, who has also played for Tottenham and Standard Liege, has previously featured in the Championship on loan for Ipswich Town and Rotherham.
He arrives after defender and captain Marc Roberts joined Birmingham.
Fryers, a left-back capped at under-16 to under-19 levels for England, is the second defender to move to Oakwell in as many days, following the signing of centre-back Ethan Pinnock.
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Championship side Barnsley have signed defender Zeki Fryers on a three-year deal after his contract with Premier League side Crystal Palace expired.