Former Southampton boss Russell Martin took over the Rangers role last month and has moved quickly to bring in his own backroom staff at Ibrox which includes goalkeeping coach Salvatore Bibbo and assistant Matt Gill.
The 41-year-old enjoyed a successful playing career, most notably spending seven years with Newcastle United where he made 150 appearances. Williamson has also been head coach at MK Dons and most recently Carlisle United lasted just under five months as his side headed towards relegation into the National League.
Speaking to the club website, Martin opened up on the appointment and his strong relationship with Williamson which will help the club perform off the pitch.
"I played with Mike at Wycombe Wanderers so we go back a long way, and I know the qualities he can bring to this group," Martin told club media.
"As a player he played at the very top level and is an experienced coach having been a manager himself.
"I am also really happy to bring Sal into the team. He has a lot of experience and a strong track record of developing goalkeepers.
"After speaking to him it was clear that his knowledge and character will be a real asset to the players and the staff, and I am looking forward to working with them both."
Rangers Sporting Director Kevin Thelwell also welcomed Williamson as Martin buillds a backroom team worthy of striving towards the title where they will compete with Celtic.
“I would like to welcome both Mike and Sal to Rangers. They are both experienced coaches who will bring a lot of knowledge to the club.
“Their addition strengthens Russell Martin’s coaching team and reflects our continued commitment to building the best environment capable of delivering success on and off the pitch.”