Beyer beat out six other candidates for the nomination.
Besides serving as lieutenant governor, Beyer also was President Barack Obama's ambassador to both Liechtenstein and Switzerland. He was endorsed by a number of Obama administration officials.
If Beyer wins in the general election he will succeed Moran, who has has held the seat for 24 years. Moran's name had previously appeared in police reports in 1999, when his then-wife phoned the police to report an incident of domestic violence. When his son pleaded guilty to assaulting his girlfriend in 2012, Moran said he hoped his son would be able to put the "embarrassing situation" behind him.