The IRFU and Munster Rugby have announced today that Williams has signed a one-year contract extension that will see him stay with the province until June 2015.
The Academy graduate moved on to a full contract at the start of the 2010/11 season and the 27-year-old has since made steady progression, providing invaluable experience in a key position.
Johne Murphy and Gerhard van den Heever are both drafted into the side on the wings with Simon Zebo moving to full-back.
Denis Hurley comes in at inside centre with Casey Laulala keeping his place outside him.
Two of the four changes in the forwards involve the front row with Ireland international props David Kilcoyne and Stephen Archer linking up with hooker Duncan Casey who will be making his fifth start for the province.
Donncha O'Callaghan and Donnacha Ryan make up the second row pairing and CJ Stander takes over from Sean Dougall in the back row alongside Tommy O'Donnell and James Coughlan who captains Munster once again from number 8.
Young Munster clubman Ger Slattery, James Cronin and BJ Botha provide front row cover on the bench, while fellow forwards David Foley and Dougall will also be keen to make an impact off the bench.
Reserve backs Gerry Hurley, who captained the Ireland Club team to two recent wins, JJ Hanrahan and Ronan O'Mahony complete the matchday 23.
Munster face the Scarlets in Llanelli on Saturday at 6.30pm. The game will be televised live on RTÉ Two and S4C with live updates here.
MUNSTER (v Scarlets): Simon Zebo; Gerhard van den Heever, Casey Laulala, Denis Hurley, Johne Murphy; Ian Keatley, Duncan Williams; David Kilcoyne, Duncan Casey, Stephen Archer, Donncha O'Callaghan, Donnacha Ryan, CJ Stander, Tommy O'Donnell, James Coughlan (capt).
Replacements: Ger Slattery, James Cronin, BJ Botha, David Foley, Sean Dougall, Gerry Hurley, JJ Hanrahan, Ronan O'Mahony.