Lawes suffered a dislocated thumb in the European Challenge Cup defeat at Gloucester on April 16 and there were fears he could miss the rest of the season.
But scans have shown that there was no fracture and Lawes has been stitched back together, with forwards coach Phil Dowson likening him to 'Frankenstein's monster' earlier this week.
Lawes has been passed fit to wear the six shirt, taking the place of Teimana Harrison in the Saints back row.
Harrison is unavailable this week, meaning trialist Aaron Hinkley is handed a place on the bench as he hopes to make his Saints debut.
Paul Hill will also be among the replacements after his wife gave birth to his second child earlier this week, meaning Conor Carey starts at tighthead.
Sam Matavesi is missing as he is playing for the Navy against the Army at Twickenham on Saturday, so Mike Haywood starts, with James Fish on the bench.
Manny Iyogun comes in at loosehead as Alex Waller drops to the bench.
Alex Coles will make his 50th Premiership appearance as he again starts in the second row, with David Ribbans again sidelined due to injury.
James Grayson comes in at fly-half, meaning George Furbank reverts to full-back and Tommy Freeman switches to the wing.
Matt Proctor, who will be making his 50th Saints appearance, also moves out wide, from centre, with Fraser Dingwall wearing the 13 shirt as he returns from injury.
Ollie Sleightholme drops to the bench, but there is no place in the squad for Tom Collins.
As for Harlequins, they are without England loosehead prop Joe Marler so Simon Kerrod starts.
Saints: Furbank; Proctor, Dingwall, Hutchinson, Freeman; Grayson, Mitchell; Iyogun, Haywood, Carey; Coles, Ratuniyarawa; Lawes, Ludlam (c), Augustus.Replacements: Fish, Waller, Hill, Moon, Hinkley, James, Francis, Sleightholme.
Harlequins: Jones; Lynagh, Marchant, Esterhuizen, Murley; Smith, Care; Kerrod, Walker, Louw; Symons, Tizard; Lewies (c), Lawday, Dombrandt.Replacements: Musk, Garcia Botta, Collier, Chisholm, Wallace, Gjaltema, Allan, David.