The 24-year-old singer said at the event in Beverly Hills that she teamed with Hudson on the capsule collection after a chance meeting with the actress in a gym.
"I met Kate while actually in the gym one time," she told People. "We connected, and I loved what she's done with Fabletics -- and here we are now!"
Fabletics will release Lovato's tops and leggings this month, with a full collection to follow in August, according to WWD. Hudson had nothing but praise for the star in an interview with InStyle at the launch.
"I love what she represents, and I think she has a very different energy, brings a different kind of energy to our company, and brings a different audience," the 38-year-old actress said.
"I think she will create a lot of buzz inside of our community for younger girls, which will be really nice. She's been very open about things in her life that she's gone through ... [and] working out and fitness and activity have been a huge part of that for her," she added.
Hudson launched Fabletics in 2013. The actress made her red carpet debut with new boyfriend Danny Fujikawa while supporting mom Goldie Hawn at the Los Angeles premiere of Snatched on Wednesday.