The TV presenter from Bray, Co Wicklow, joins former British shadow chancellor Ed Balls and singer Will Young, who were announced earlier this week.
Whitmore, 31, joined Nick Grimshaw live on the BBC Radio 1 Breakfast Show for the announcement.
“I’ve always known I wanted to do it, but I was waiting for the right time,” Whitmore told Grimshaw, explaining that she had previously had to turn down the opportunity due to other commitments.
The third Strictly Come Dancing contestant said she was an enthusiastic dancer, but admitted: “I like to dance but there’s no training involved.”
She added: “When I was a kid, I Irish-danced, but not well... It was just the legs that moved. Apparently now I have to use my hands as well.”
Whitmore, who presented spin-off I’m A Celebrity...get Me Out Of Here Now! from 2011 to 2015, said her mother was very excited to see her on the BBC show, adding: “That’s what she’s always wanted me to do.”
Whitmore, who was given the Shakespearean code name Lady Macbeth to keep her identity secret before the announcement, said she was relieved the truth was out.
She joked: “I can tell my mum, I’ve been lying to her all these months! Well she kind of knows. She’s already booked the plane ticket.”
On what she is looking for in a professional partner when she gets paired up later in the month, she said: “I just want someone who can lift me.”
Whitmore said she had already been in to try on the costumes — which transformed her. “I am not a huge sequins person... but do you know what, I am going to embrace the sequins,” she said. “The minute you put it on, suddenly I’m not Laura any more, I’m this other person.”
She told Grimshaw she planned to throw herself into training, promising: “I’m going to come in here in December and I’ll be like the Hulk.”