The 24-year-old singer-songwriter from Hitchin, Hertfordshire, has impressed music industry experts with his sell-out gigs to tens of thousands of people in the past few months. He has also supported high profile performers John Newman and Tom Odell.
Bay will release his debut album in the spring and perform at the Brits nomination party next month along with Clean Bandit and FKA Twigs.
“I’m pretty speechless,” he said. “After all the years I’ve spent watching the Brits and even after this year; watching my fan base grow so much, I never thought I’d actually be getting an award myself.
“What a huge honour to be following the incredible artists who’ve won before. I’m really chuffed, thank you to everyone who has supported me.”
Past Critics’ Choice winners have included Sam Smith, Adele, Jessie J, Ellie Goulding, Emeli Sande and Florence + The Machine.
The Brit Awards 2015 will be staged at the O2 Arena in London on 25 February. Ant and Dec are replacing regular host James Corden and Tracey Emin has designed the statuette.