Pulis was appointed West Brom's manager on January 1 and moved towards a more settled support staff on Tuesday, with Francis joining Dave Kemp as an assistant coach, while Paul Jewell decided to end his short-term stint at The Hawthorns.
Jewell only joined West Brom last week.
Francis - a former England captain - helped Pulis lead Palace to Premier League safety last season, while they also worked together at Stoke from 2008 until Pulis was shown the door in 2013.
"Gerry and I have worked well together at both Stoke and Crystal Palace and it was always part of my plan for him to join me at Albion," Pulis said in a statement on West Brom's website.
"I value his insight and experience of the very highest levels of our game and I'm delighted that he is now on board. We have an agreement that we have employed in the past and suits us both."
Francis was all business when asked about joining West Brom.
"I like the set-up. Albion have a good training ground, good facilities but, just as was the case at Stoke and Palace, it's vitally important for the club to retain Premier League status," the 63-year-old said.
"There's going to be a number of teams involved in the situation. We've had three decent results but there's a lot of work to do with the side and Tony is obviously looking to strengthen if he can.
"But I'm looking forward to the challenge."
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