Finneas O’Connell and Claudia Sulewskiare officially married — and his superstar sisterBillie Eilish had one very important job on their big day.

The Grammy-winning musician and producer and the actress/creator tied the knot in an intimate ceremony at the luxe San Ysidro Ranch in Santa Barbara, Calif. … surrounded by family, famous friends and even a couple of their four-legged favorites.

Billie officiated the ceremony, while Finneas and Claudia’s dogs, Peaches and Moose, also got in on the celebration. Their parents, Maggie Baird and Patrick O’Connell, were there to watch their son exchange vows.

According to Vogue, Sulewski wore four Oscar de la Renta wedding weekend looks … one for the rehearsal dinner, the ceremony, first dance and reception dress, and the after party.

The guest list was stacked … Justinand Hailey Bieber, Rachel Sennott, Emma Chamberlain, Rebecca Black, Jason Sudeikis, Kristen Bell, Dax Shepard, Devon Lee Carlson, Stassie Karanikolaou, Jesse Jo Stark and more all turned out for the newlyweds.

Billie arrived with Nat Wolff, and the two stayed close throughout the festivities.

There was also a moment involving Justin and Hailey that caught some attention — the pair stepped away from the crowd for what appeared to be a serious, emotional conversation.

Justin later took a phone call, and Hailey walked back over to rejoin the party.