The young attacker extends his stay with Northern Premier League side Guiseley AFC until January 2 2023.
Joining initially for a month at the start of November, the 18-year-old will spend the rest of this calendar year at Nethermoor Park.
The youngster has made two appearances for the Reds so far this season, both coming in Papa John's Trophy Group E victories against Newcastle United U21s and Doncaster Rovers.
Hartley recently signed a professional deal with the Reds, after last year being part of the successful U18s side that finished second in the Professional Development League and narrowly lost out to Charlton Athletic in the PDL Play-Off final.
Everyone at Barnsley FC wishes Keegan well during his time out on loan!
