MacRae told Digital Spy that he had been impressed by the 26-year-old star's original audition tapes.
"She just had this amazing energy," he explained. "She's actually a couple of years older than Karen [Gillan] but she seems younger - she seems more of a teenager and bouncy. She's fantastic.
"It's really hard to take over from any companion that's loved like Amy and Rory are, and she's just going to be so different whilst still being a Doctor Who companion. It's a very good choice from the producers."
MacRae also confessed that he had been aware of Coleman's surprise guest appearance in Who's series seven premiere 'Asylum of the Daleks' prior to transmission.
"I was amazed that it stayed secret, but thrilled that it did," he revealed. "It was a very clever decision of Steven [Moffat]'s to tease in that way, because he's given away absolutely nothing but created a lot of interest."
MacRae's most recent contribution to Doctor Who was 2011's 'The Girl Who Waited', with the writer admitting that he had been overwhelmed by the "extraordinary" reaction to the episode.
"It got just incredible, incredible reviews," he said. "I don't think Doctor Who fans liked me very much before that, because I was very young when I got the job and I think they thought I hadn't really earned it.
"So I worked really hard to do something that would prove the point that I had the right to sit at that table, and then everyone just loved it and I couldn't believe it. I was so overwhelmed."
However, he refused to confirm if he would be contributing a new Doctor Who episode for the show's initial 2013 run.
"I can tell you there are some unconfirmed spots, but I can't say anything more than that," he stated.
MacRae's sitcom Threesome returns to Comedy Central for a second series on Monday, October 1 at 9.30pm. Doctor Who continues this Saturday (September 29) on BBC One and BBC America.
> Tom MacRae Threesome Q&A: 'Series two is going to be different'
Watch the cast and crew of Doctor Who discuss new star Jenna-Louise Coleman below: