Chapman, 18 has become Chris Wilder's eighth summer signing after joining on loan from Premier League Middlesbrough and could make his debut at home to Rochdale tomorrow.
The England Under-18's International spent time on loan at near neighbours Barnsley, helping the Tykes to double Wembley success in the Johnstone's paint Trophy Final win over Oxford United and the SkyBet League One Play-Off Final win over Millwall.
Wilder told sufc.co.uk; "Harry is a highly-rated wide player with plenty of ability and I'm sure he's going to excite our supporters."