Bath start their eight players called up to the England squad on Thursday, including Sam Underhill and uncapped duo Tom de Glanville and Max Ojomoh.
Northampton make nine changes, with their England call-ups Fraser Dingwall, Paul Hill, skipper Lewis Ludlam and Alex Mitchell all in their XV.
Chris Boyd's side will finish fifth in the Premiership whatever the result.
Eighth-placed Bath, however, could move up as high as sixth if they win at The Rec and other results go their way.
As well as Priestland, Christian Judge, Henry Thomas, Will Chudley and Zach Mercer - who will play his 100th club match from the bench - will also make farewell appearances for the hosts.
Bath: De Glanville; Watson, Joseph, Ojomoh, Cokanasiga; Priestland, B Spencer; Obano, Du Toit, Judge, McNally, Ewels (capt), Reid, Underhill, Faletau.
Replacements: Doughty, Schoeman, Thomas, W Spencer, Mercer, Bayliss, Chudley, Bailey.
Northampton: Freeman; Collins, Dingwall, Hutchinson, Naiyaravoro; Grayson, Mitchell; Auterac, Haywood, Hill, Coles, Moon, Lawes, Ludlam (capt), Wood.
Replacements: Fish, Waller, Painter, Ratuniyarawa, Newman, Tupai, Proctor, Gillespie.