The personal finance website was established by Lewis, a financial journalist, in 2003.
According to Google Analytics, the MoneySavingExpert website attracted about 39m unique visitors and approximately 277m page impressions in the year ended 31 October 2011.
In the year ended 31 October 2011, MoneySavingExpert reported revenues of £15.773m (2010: £11.361m) and EBITDA of £12.642m (2010: £8.379m).
On completion, Martin Lewis will become an employee of the MoneySupermarket group and his role will be editor-in-chief of MoneySavingExpert.
MoneySupermarket intends to preserve the editorial independence – free of commercial considerations – of MoneySavingExpert.
In order to ensure this MoneySupermarket and MoneySavingExpert have agreed an editorial code.
Lewis said: “I chose MoneySupermarket to work with as I know and trust them. They understand the site, as they’ve shown by agreeing the editorial code, which ensures our content can proudly remain editorially independent and free from commercial considerations.”
Lewis is set to give £10m to charity when the deal completes, including £1m to Citizens Advice.