Romaine Sawyers has returned to West Brom from Brentford, for an undisclosed fee.
The 27-year-old returns to The Hawthorns after leaving in 2013 and has signed a three-year deal, with the option of a further 12 months, after completing a medical on Friday.
He had been a long-term target for Albion after impressing for Sky Bet Championship rivals Brentford over the last three years.
Sawyers told West Brom's official website: "It's been a long time coming and feels like I have unfinished business."
"This is the first team that I have always wanted to play for and I'm delighted I'm now going to get that chance.
"I left the club when I was just a boy with a lot of potential. But I am coming back as a man who has matured as a player.
"It looks to me that we are assembling a strong group of players and I hope to add to that.
"The aim is promotion – that's what we all want especially after just missing out last season."
Celtic and Aston Villa had been interested, with the Hoops having a £2million bid rejected earlier this month.
New Albion boss Slaven Bilic gave the green light for the move after doing his own due diligence on the attacking midfielder.
Sawyers initially left the Baggies on a free six years ago after coming through the youth ranks but did not make a senior appearance.
He joined Walsall on a permanent deal after an initial loan and spent three years at the Banks's Stadium before joining Brentford on a free transfer.
The St Kitts and Nevis international made 135 appearances for the Bees, scoring eight goals.
West Brom had been looking to boost their attacking ranks after signing Kenneth Zohore from Cardiff having lost Jay Rodriguez to Burnley and seen Dwight Gayle's loan from Newcastle end.
