“I love my husband more than my job,” she said.
Speaking to presenters Jon Kay and Sally Nugent, she said: “I didn’t want to get emotional, but you two are my friends, and I love you dearly.”
Asked about an end to early-morning starts, she joked: “What is a lie in? I have no idea. Alarm clocks will be a thing of the past.
“This hasn’t been an easy decision to make, but it feels like the right moment to step away,” she said. “I’ll carry with me the most wonderful memories.”
Kirkwood received her meteorological training at The Weather Channel, the Met Office and the BBC, before joining the BBC Weather Centre in April 1998.
She began broadcasting on the BBC News channel, and went on to appear regularly on BBC One. She has been the main weather presenter on BBC Breakfast since 2010.
Kirkwood said it had been an “absolute privilege” to bring viewers the weather every day.
“My job is something I’ve never taken for granted and I’ve loved every minute,” she said.
“To those watching and listening at home – thank you for all the kindness you have shown me over the years, being part of your mornings has been a joy.”