The 21-year-old, who can also play in midfield, has agreed one-year deal with the option of a further 12 months.
The England Under-20 international and Tykes youth product played six times for Mick McCarthy's side after joining on a temporary basis in January.
Digby had previously made 25 appearances for Barnsley.
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Championship side Ipswich have signed defender Paul Digby on a free transfer from Barnsley, after he finished last season on loan at Portman Road.