Pardew returns to management for the first time since being sacked by Crystal Palace in December 2016 and replaces Tony Pulis at West Brom.
Pulis was sacked earlier this month with West Brom hovering above the relegation zone after four straight league defeats.
“I‘m thrilled with the opportunity Albion have provided and looking forward to getting to work with what I consider to be a talented group of players,” Pardew said on the club website. (www.wba.co.uk).
“The immediate challenge will be to get the results we need to pull ourselves up the table. But I‘m aware that while I‘m joining one of the great, traditional clubs of English football, it is one (that is) determined to go forward in the Premier League.”
West Brom chairman John Williams said the 56-year-old was the unanimous choice for the job.
“Alan brings the experience of more than 300 Premier League games and the kind of dynamic leadership from which our club can benefit,” he said.
Pardew was named the Premier League’s manager of the year for guiding Newcastle United to fifth in the 2011-12 season.
Meanwhile, caretaker boss Gary Megson left his role as assistant coach after leading the team to draws against Tottenham Hotspur and Newcastle in their last two games.
Pardew will take charge of his first game on Saturday and comes up against basement side Crystal Palace.
He had guided them to 10th in the 2014-15 season for their best Premier League finish and followed that up with a 15th-placed finish.