Halsey says she has "no tolerance for a lack of inclusivity" after performing at the Victoria's Secret fashion show.
The underwear brand was criticised last month after its chief marketing officer said they shouldn't have trans people in their shows.
The show was recorded before the comments were published, but only broadcast on Sunday night.
Halsey posted on social media: "If you a trans person reading this... please know that you have allies."
Ed Razek told Vogue in November: "Shouldn't you have transsexuals in the show? No. No, I don't think we should."
He added: "The show is a fantasy. It's a 42-minute entertainment special. That's what it is. It is the only one of its kind in the world."
He later apologised after a backlash, saying: "To be clear, we absolutely would cast a transgender model in our show.
"We've had transgender models come to castings... And like many others, they didn't make it."
In her statement, Halsey said: "Complete and total acceptance is the only 'fantasy' that I support".
She added that "as a member of the LGBT+ community, I have no tolerance for a lack of inclusivity. Especially not motivated by stereotype."
The 24-year-old singer also said: "I have adored the Victoria's Secret fashion show since I was young."
She performed alongside the likes of Shawn Mendes, Bebe Rexha and The Chainsmokers.
Models at the show included Kendall Jenner, Gigi and Bella Hadid and Winnie Harlow.