The model, 21, and the pop star, 24, were reported to have tied the knot in secret in September, two months after they got engaged.
Baldwin, who has 15.4 million followers on Instagram, has changed her handle to @HaileyBaldwin and her bio to read Hailey Rhode Bieber.
Canadian singer Bieber has also seemingly confirmed the rumours, calling Baldwin his wife in a post on his own page.
He shared a picture of the pair together with the caption: "My wife is awesome."
The couple were rumoured to have married in a New York courthouse two months ago, but Baldwin denied it at the time.
Baldwin, the daughter of actor Stephen Baldwin, and Baby hitmaker Bieber announced their engagement in July.
The singer wrote on Instagram: "Hailey I am soooo in love with everything about you!
"So committed to spending my life getting to know every single part of you loving you patiently and kindLY.
"My heart is COMPLETELY and FULLY YOURS and I will ALWAYS put you first! You are the love of my life Hailey Baldwin and I wouldn't want to spend it with anybody else. You make me so much better and we compliment each other so well!!"