The 30 Rock and Saturday Night Live star revealed the news in a red carpet interview before Monday’s Emmy awards in Los Angeles.
The Hollywood actor told Access “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”.
Asked what advice he would give his new nephew-in-law, the 60-year-old star, whose brother is Hailey’s father Stephen, said: “Keep working … don’t stop working”.
The US model, 21, and Canadian singer, 24, were spotted at the marriage bureau at a courthouse in New York City last Thursday, prompting the model to deny wedding rumours.
In a since-deleted social media post, she wrote: “I understand where the speculation is coming from, but I’m not married yet!”
But an insider told People last week that the couple “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,” the source added.
Bieber popped the question to the model in July, around four months after splitting from previous girlfriend Selena Gomez.
The pop star expressed his love for Baldwin in a long Instagram post in which he called her “the love of my life”.
She responded with equally fulsome praise of her partner, telling him in a tweet: “Not sure what I did in life to deserve such happiness but I am so utterly grateful to God for giving me such an incredible person to share my life with!”
The reported newlyweds have been in the UK after Baldwin arrived for London Fashion Week where she attended the launch of her Adidas collection on Monday.