The banjo player from folk-rock group Mumford & Sons said he is "taking time away from the band" following criticism for praising a conservative writer.
Winston Marshall caused controversy after tweeting support for US journalist Andy Ngo over the weekend.
In a since-deleted post, Marshall said he had read Ngo's "important" bookand praised him as a "brave man".
Fans of Mumford & Sons, a chart-topping band formed in London in 2007, were quick to share their disappointment at the endorsement.
One described Marshall's tweet as a "dumbfounding endorsement of fascism".
In a statement on Twitter, Marshall, 33, said he is stepping away from the band to "examine my blindspots".
Marshall, son of wealthy British investor Sir Paul Marshall, added: "For now, please know that I realise how my endorsements have the potential to be viewed as approvals of hateful, divisive behaviour. I apologise, as this was not at all my intention."
Ngo's bookclaims to expose a "violent extremist movement". Critics say it inflates the size and threat of the left-wing antifa movement, which was a frequent target of Donald Trump.
Thedescribes the book as "supremely dishonest".
The remaining members of Mumford & Sons are Marcus Mumford, Ben Lovett, and Ted Dwane. Their best-known songs include 'I Will Wait' and 'Little Lion Man'.
Representatives for the band have been contacted for comment.