League sources told ESPN and NFL Media that Campbell is receiving a six-year contract from the Lions. The team, which will introduce Campbell with a news conference Thursday, didn't disclose terms of the agreement.
"This is an exciting day for our organization as we introduce Dan Campbell as the new head coach of the Detroit Lions," Lions principal owner Sheila Ford Hamp said in a statement. "With more than 20 years of experience as both a coach and player in the National Football League, Dan knows the rigors of professional football and what it takes to be successful.
"He will help promote the culture we want to establish across our organization, while also bringing with him high energy, a respect for the game and an identity with which everyone can align themselves."
Campbell, who served as the Saints' assistant head coach and tight ends coach, replaces Matt Patricia, who was fired in November after less than three seasons with the Lions. He posted a 13-29-1 record as Detroit's head coach.
The 44-year-old Campbell is expected to bring fellow Saints assistant coach Aaron Glenn with him to be the Lions' defensive coordinator, according to multiple reports.
Before joining the Saints, Campbell was a coaching intern with the Miami Dolphins in 2010. He later moved up to tight ends coach and served as the team's interim head coach in 2015 after the firing of Joe Philbin. The Dolphins posted a 5-7 record under Campbell.
Campbell played 10 seasons in the league, including the final three years of his career with the Lions.