The former Olympic athlete, who finished third in this year's I'm A Celebrity...Get Me Out Of Here!, will host Fatima's Fat Fight on the ITV1 daytime show from Thursday.
The segment will see Whitbread help four obese volunteers get back into shape over a 12-week period, with Dr Chris Steele and Amanda Hamilton helping along the way.
A show source told The Mirror: "Fatima has 12 weeks to help the overweight This Morning fans - and the hope is people at home will join in. It could lead to a whole new career. Producers have already dubbed her Mrs Motivator."
This Morning's editor Adam Vandermark added: "Fatima showed us her steely toughness on I'm A Celebrity, so she is the ideal person to get our four overweight viewers back into shape."
Whitbread recently admitted that her stint on I'm A Celebrity helped her to find herself again.