US President Barack Obama was into the fourth year of his term before he publicly endorsed gay marriage.

But if Maroon 5 singer Adam Levine were the nation's chief executive, it would only take a single day.

Levine, promoting his group's new album Overexposed, was asked by MTV what he would do if he were president for a day.

'First I'd make gay marriage legal because that's just archaic and ridiculous,' he said. 'That's the first thing I would do. If I'm only going to be be president for a day, you gotta get in and out and make some changes.'

Levine's support of LGBT equality is well known and The Voice, the NBC competitive reality show on which he is a mentor, has also been very gay inclusive since its debut last year.

'I think we always supported and nurtured all the amazingly talented people who have been in the show regardless of what they do in their private time,' Levine told Gay Star News earlier this year.

'I think there's absolutely no reason why you should be judged for your sexuality,' he added. 'It's your choice to be vocal about it, to be quiet about it. Sexuality is a very personal thing. If you want it to be public knowledge, put it out there or you can keep it wrapped up.'