The Money Saving Expert star will host the ITV show alongside Susanna Reid on various Wednesdays this year.
“To have the ability to hold politicians to account, over the cost of living, is a privilege and a responsibility,” he said as his new role was announced.
The journalist and broadcaster – who has already been a guest presenter on the programme – will kick off with a tax year end special on Wednesday, 29 March.
Lewis said: “It’s a slight gear change from my usual work, but after years of answering complex questions, it’s nice for once to be asking them. So I was delighted when ITV offered me the role of regular presenter.
“The difficulty came with working it around my day job, as Money Saving Expert, which is always my priority.
"So I’m hopeful the solution we’ve come up with, to lock in a dozen special shows a year, sitting alongside Susanna Reid’s brilliant journalism, is one the show’s viewers will welcome.”
Reid said Lewis was "undoubtedly the voice of the nation when it comes to the cost of living crisis".
"Together we will continue to challenge politicians and hold them to account," she went on.
"I can’t wait to have him sitting next to me again at the GMB desk from next week.”
Emma Gormley, managing director ITV Daytime, added: "As Good Morning Britain continues to answer the questions the nation wants and needs answering each weekday morning, we’re thrilled to welcome Martin Lewis as a regular co-host.”
Martin Lewis is on Good Morning Britain from Wednesday 29 March at 6am on ITV1 & ITVX.
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