The specialist dance DJ told Digital Spy that she was excited about Grimshaw's stint as the new host, which starts this Monday (September 24).
"It's brilliant - I was so happy when I heard the news," Mac said.
"It's something that I personally wanted to happen but I never really thought Radio 1 would be brave enough to make that decision."
She continued: "It's kind of a risk, but that's why it's exciting because Grimmy will be great and he'll maybe say the wrong thing and he'll maybe stay up all night one night.
"He'll genuinely be irreverent and anarchic - in the same vein as Chris Evans or whatever - and I think that makes for exciting radio and it's important to listen.
"He is just brilliant on the radio. He loves a chat, he's got the best work ethic of anyone I've ever met. He works really hard and never moans.
"In terms of having to keep those hours, of all the people I know he is the one that will be alright."
Of the debate on whether Moyles is a fan of music, Mac said: "I think he does like music. He just likes The Verve and Oasis and the music that he plays in that last hour of his show.
"He's genuinely a massive music fan, but maybe not [as wide a range] as Grimmy."
She added: "Grimmy's got impeccable taste in music. I don't think he's given a lot of credit for the music that he played on his evening shows, it was really, really high quality.
"I don't if he's going to be able to bring that the breakfast show. He definitely will play a lot more music and I think the breakfast show will have a real different element, and maybe a better one."
> Nick Grimshaw breakfast show will be exciting, says Huw Stephens
> Nick Grimshaw right for BBC Radio 1 breakfast show, says Gemma Cairney
Asked if she would ever host the breakfast show herself, Mac said: "No, I think I've kind of made a name for myself as being a music curator and I think it would be kind of weird to go to the breakfast show and play playlisted pop music.
"All the work I've put into being hopefully trusted and respected for playing good music, it would be weird to just go and play whoever - and those hours are not the ones for me!"
Annie Mac releases Annie Mac Presents 2012 on October 8. It is available for pre-order now.
She takes the AMP 'All The Way' tour on the road in November and December, with guests Magnetic Man, Redlight, Rudimental and Disclosure.