In a statement on his Web site, Campbell said Friday that "management difficulties, which have been ongoing for almost five years, had become intolerable."
"No words can express how upset I feel today that I have been forced to make this decision," he wrote.
UB40 was founded in Birmingham, central England. The band fused reggae and pop to popular effect, notably on hit versions of "Red Red Wine," "I Got You Babe" and "(I Can't Help) Falling in Love With You."
The band was named after Unemployment Benefit Form 40, the government document used by welfare claimants.
Campbell said UB40, which includes his brother Robin, would continue without him.
In a separate statement, UB40 said Campbell "has taken the decision to focus on his solo career and in doing so, could not give his full commitment to UB40."
"The other band members of UB40 are naturally disappointed and saddened after being together as a band unit and as good friends for almost 30 years," the statement said.
UB40's upcoming "24/7," which was recorded with Campbell, will be released as planned in May.
