Williams is the only player from the British Isles in the starting XV but is joined in the squad by Wales and Cardiff Blues team mate John Yapp, who takes a place on the bench.
Australian Matt Giteau will lead the invitational side which is made up of largely South Hemisphere stars against the World Champions.
Uncapped South African lock Anton van Zyl will line up against his fellow countrymen while New Zealander Colin Bourke is the only other player included without International experience.
Barbarians: James O’Connor (Aus); Joe Rococoko (NZ), Drew Mitchell (Aus), Adam Ashley-Cooper (Aus), Ma’a Nonu (NZ); Matt Giteau (Aus, capt), Will Genia (Aus); Salvatore Perugini (It), Stephen Moore (Aus), Neemia Tialata (NZ), Anton van Zyl (Stormers), Chris Jack (NZ), Rodney So’oialo (NZ), Martyn Williams (Wales), Colin Bourke (Chiefs).
Replacements: Keven Mealamu (NZ), John Yapp (Wales), Quintin Geldenhuys (It), Daniel Braid (NZ), Andy Ellis (NZ), Stephen Donald (NZ), Seru Rabeni (Fiji).
