The IRFU and Munster Rugby are delighted to announce 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 a 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 first centre with Casey Laulala keeping his place at second centre.
Two of the four changes in the forwards involve the front-row with Irish international props Dave Kilcoyne and Stephen Archer joining hooker Duncan Casey who maintains his place to make his fifth start for the province.
O'Callaghan and Ryan make up the second-row and CJ Stander takes the place of Sean Dougall in the back-row with Tommy O'Donnell keeping his place and Coughlan captaining the side from no.8 once again.
Young Munster's Ger Slattery, James Cronin and BJ Botha provide the front-row cover with Dave Foley and Dougall also ready to make an impact off the bench.
Gerry Hurley, JJ Hanrahan and Ronan O'Mahony are the three backs named in the replacements.
Munster face Scarlets at Parc y Scarlets on Saturday at 6:30pm. The game will be televised live on RTE and S4C with live updates here.
Munster are back in action at Thomond Park next month with more details here.
Munster: Simon Zebo; Gerhard van den Heever, Casey Laulala, Denis Hurley, Johne Murphy; Ian Keatley, Duncan Williams; Dave 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, Dave Foley, Sean Dougall, Gerry Hurley, JJ Hanrahan, Ronan O'Mahony.