The 23-year-old has come off the bench in both of Scotland's opening two matches in the competition to date, including last weekend's comprehensive victory over England at Scottish Gas Murrayfield.
Matt Fagerson is also restored to the starting lineup for Saturday's clash in Cardiff, the back-rower coming in to start at number eight in place of the injured Jack Dempsey to win his 62nd cap in the dark blue jersey.
Gregor Brown shifts from the second-row to the blindside flank in order to accommodate Williamson's inclusion, with Rory Darge continuing at openside having won more turnovers than any other player in the opening two rounds of the Guinness Six Nations.
Scott Cummings joins Williamson in the engine room, whilst Zander Fagerson and Nathan McBeth - who made his first Guinness Six Nations start last weekend - are retained as the starting props for the visit to the Principality Stadium.
Behind the scrum, Kyle Steyn continues on the wing after a Player of the Match-winning performance at Scottish Gas Murrayfield, sitting joint-top of the charts for defenders beaten across the opening two fixtures.
Sione Tuipulotu once again captains the side from inside centre, partnering Huw Jones - scorer of a brace of tries in last weekend's victory - in the midfield.
George Horne completes the Glasgow contingent in the matchday 23, the scrum-half the sole Warrior selected amongst the replacements for Saturday's match.
Scotland
15 Blair Kinghorn - Toulouse (63)
14 Kyle Steyn - Glasgow Warriors (30)
13 Huw Jones - Glasgow Warriors (60)
12 Sione Tuipulotu - Glasgow Warriors (35) - Captain
11 Duhan van der Merwe - Edinburgh Rugby (52)
10 Finn Russell - Bath Rugby (91) - Vice-captain
9 Ben White - Toulon (33)
1 Nathan McBeth - Glasgow Warriors (7)
2 Dave Cherry - Vannes (17)
3 Zander Fagerson - Glasgow Warriors (78)
4 Max Williamson - Glasgow Warriors (11)
5 Scott Cummings - Glasgow Warriors (47)
6 Gregor Brown - Glasgow Warriors (14)
7 Rory Darge - Glasgow Warriors (36) - Vice-captain
8 Matt Fagerson - Glasgow Warriors (61)
Substitutes
16 George Turner - Harlequins (52)
17 Pierre Schoeman - Edinburgh Rugby (46)
18 Elliot Millar Mills - Northampton Saints (13)
19 Grant Gilchrist - Edinburgh Rugby (85)
20 Josh Bayliss - Bath Rugby (14)
21 George Horne - Glasgow Warriors (42)
22 Tom Jordan - Bristol Bears (14)
23 Darcy Graham - Edinburgh Rugby (52)