Dike impressed for fellow Championship side Barnsley on loan last season, striking nine times in 21 appearances as Valerien Ismael's former club made it into the play-offs.
Barnsley ultimately faltered in its semi-final against beaten finalist Swansea City, but Dike has now followed Ismael to West Brom on a four-and-a-half-year contract.
The 21-year-old striker also registered 11 goals for Orlando in 19 MLS outings in 2021, drawing reported interest from Premier League sides Leeds United, Newcastle United and Everton.
However, Ismael and the Baggies managed to secure a deal for Dike on Sunday (AEDT), subject to international clearance, for a fee believed to be around £7 million ($13 million).
The West Brom manager believes his new signing can fire his side back into the Premier League.
"I'm delighted we have completed the transfer of Dike," Ismael said. "He was always our first target and priority.
"There's a lot of teamwork that has gone into this deal. Dike has everything we need from the No.9 position. He has energy, strength – he challenges defenders – and he scores goals.
"I worked with him at Barnsley and I know him very well. He has the mentality. He is 21 and is still a young player – but he has a lot of experience.
"Now it's about preparing Dike for the Championship. It was important to us to get Dike as early as possible because we know that he had four weeks off after the MLS season.
"For sure, he needs time and the schedule for him is to work hard in the next two weeks, so he is ready to play a part against QPR [on 16 January AEDT]. That is our target and now, with my staff, we will work to have a very, very good build-up – using every day – to ensure he is in top shape by that game."
West Brom currently sits fourth in the Championship, four points adrift of second-placed Fulham and eight points behind leader Bournemouth.