Diplo had one hell of a night in Vegas ... with a lot of famous friends in the mix.
The DJ capped off an action-packed Thursday in Sin City by DJing a show at Wynn's Encore Beach Club ... which served as the official after-party of the 2019 Billboard Music Awards.
Among the celebs who joined him onstage was Halsey -- who also performed at the BBMAs -- and she rocked a couple of her hits live, "Closer" and "Bad at Love." She told the crowd she was going big or going home ... and they ate it up.
Speaking of going big, Diplo's late-night set came after he attended the awards show at the Grand Garden Arena and then made his way over to the Little White Wedding Chapel ... to be one of the select few guests at Joe Jonas and Sophie Turner's surprise wedding.
As we reported ... the couple got married by Reverend Elvis after the Jonas Bros performed just hours earlier at the BBMAs. Diplo captured the ceremony on his Instagram Live.
So, he can add wedding videographer to his resume.