Before heading into the venue, Lovato -- a longtime advocate for the LGBT community -- chatted with ET on the red carpet, where she got candid on the importance of accepting others.
"Honestly, I'm just doing what already needs to be done," the 23-year-old pop star explained. "I'm just talking about accepting yourself, making it easier for people to love who they are, and hopefully helping society just accept who they are."
Today, Lovato is more confident than ever, but growing up as a young star in the spotlight, she didn't always feel that way. The former Disney star has been extremely vocal about her struggles with bipolar depression and an eating disorder. The "Confident" singer admitted that if she could go back in time and tell her younger self that everything would be OK, she would.
"I would tell my younger self, 'Love who you are. Love yourself, and you're beautiful,'" she said.
During the ceremony, Nick Jonas presented Lovato with the prestigious Vanguard Award, which honors "media professionals who have made a significant difference in promoting equality and acceptance." She told ET that it felt "amazing" to have her longtime friend present her with the award.
"He's so supportive all the time," she gushed. "I could never get tired of him."
Onstage, Lovato was quite the jokester, poking fun at her bestie's package while accepting her award.
"What people don't know about me is, I know that you all love Nick Jonas, but I actually have a bigger d**k than he does," she joked. "And a huge set of balls. I'm going off script, by the way."
But Jonas wasn't the only one that got a special shout-out from Lovato. She also thanked her boyfriend, Wilmer Valderrama, though her message to him was a tad bit sweeter.
"Thank you to my love who can't be here tonight. He's shooting a pilot," she explained. "I'm just extremely proud of him. His name is Wilmer Valderrama and I'm so proud to be his girlfriend -- for accepting me as the woman that I am."
"And even though I'm with him, it's just so important to be who you are," she continued. "Love is fluid, gender is fluid. I'm getting a cat next week-- I'm getting a p***y next week and naming it Harry because equality."
Jenner -- who was dressed in a gorgeous red gown and strappy silver heels -- also won big. Her reality TV series, I Am Cait, tied with TLC's I Am Jazz for Outstanding Reality Program, beating out Discovery Life's New Girls on the Block, Oxygen's The Prancing Elites Project and Fuse's Transcendent.
Lovato later took to Instagram on Sunday to share a few snaps from her exciting night.
"Last night I was given the Vanguard award from GLAAD and one of my best friends presented it to me with words that totally made me cry," she wrote. "That friend is my brother @nickjonas and I'm so thankful for our friendship. Love you and thanks for last night."
She followed it up with a collage of the two at the GLAAD Awards in 2008 and at at this year's ceremony, and it could not be any cuter.
"Love this!!" she captioned the Instagram re-share, adding the hashtags, "#8yearslater" "#Somethingsneverchange" and "#besties."
Orange Is the New Black star Ruby Rose was also honored at the GLAAD Awards -- which air Monday at 10 p.m. ET on Logo. The Australian actress received the Stephen F. Kolzak Award and her close pal, Taylor Swift, made a surprise appearance at the show to present her with the award.