The Cameroon defender moves to The Hawthorns on a four-year contract.
The 28 year-old made 32 appearances last season for Quique Sanchez Flores' side and kept nine clean sheets, with one assist.
Tactical change sees Nyom drop out
Following yet another managerial change over the summer at Vicarage Road however, The Hornets' new boss Walter Mazzari has tinkered with his system.
Instead of utilizing Flores' 4-4-2 set-up, the Italian has adopted a more traditional modern Italian sweeper model, with three centre-backs and two wing-backs.
With winger Nordim Amrabat used as the right wing-back, Nyom has been an unused substitute for Watford and is yet to play a minute this season.
'Premier League one of best in world'
As a former Serie A player with Udinese himself, Mazzari's decision to leave out Nyom is perhaps a puzzling one, however the Cameroon international's comparative lack of pace down the flanks is a supporting argument.
Speaking on his arrival at West Brom, Nyom said, "I received a call from my agent last night and he told me about the offer to come here and I was happy to do so."
The Cameroonian explained how he enjoyed his first season in England stating, “Last year was my first in England. I was so happy to play in the Premier League", regarding it "one of the best leagues in the world. I enjoyed it a lot."
"The Premier League is completely different to other leagues" Nyom finishes, saying there is "more intensity, more fight... the atmosphere in England is better than Spain."
In making the move to the West Midlands, Nyom will provide competition for Craig Dawson at right-back but could also find a spot in central defence next to Gareth McAuley.