Hailey Baldwin and Justin Bieber. Picture: Supplied

Justin Bieber and Hailey Baldwin got married on the day they received their marriage license.

The 'Baby' singer and his model partner were rumoured to have tied the knot last month, but the 21-year-old beauty dismissed the reports.

However, according to TMZ, Justin's friend Josh Mehl was a witness at their wedding ceremony on September 13, which was officiated by preacher Jeffrey Quinn, a member of the faculty at Nyack College, which is near the courthouse in New York City.

The couple also spoke to lawyers about drafting a prenuptial agreement - but they didn't do so until the day they got married, meaning there was no time to get the paperwork in place and signed in time.

And Justin and Hailey have made no attempts to get a postnuptial agreement signed instead, as the 24-year-old singer is "so in love" he doesn't feel the need for one, despite having an estimated fortune of $250 million.

The couple are still planning on a formal ceremony, but it will be a wedding in name only as they are already husband and wife.

Hailey previously denied having married Justin on Instagram.

She wrote: "I understand where the speculation is coming from, but I'm not married yet!"

However, days later her uncle Alec Baldwin claimed his niece and the 'Love Yourself' hitmaker had "just went off" and got married.

He said: "They just went off and got married and I don't know what the deal is. We text Hailey every now and then. We met him one time." 

It was previously claimed the pair have tied the knot but won't consider themselves officially married until they hold a religious ceremony.

A source said: "They went ahead and did it without listening to anyone. They're going to have a big blowout, in front of God and everyone they love."