The actor has been relying on the sport for less than a year after deciding that he wanted to slim down, The Sun claims.
McFadden, who plays hardman Phil Mitchell on the BBC One soap, will now put his training to good use by taking part in the British Gas Great North Swim on September 13. The challenge will see him swimming in Lake Windermere in order to raise money for the RNLI.
"To take part in the Great North Swim and help the RNLI is a privilege for me," the 50-year-old explained. "I love swimming but to do a mile on Lake Windermere is not only a challenge but my idea of a great day out."
The event's project manager Colin Hill added: "Swimming is a weight-bearing exercise - your bulk is supported by the water - so you're not putting excess weight on your joints and bones. And you're working all the major muscles in your body. This makes it an excellent way to lose excess weight.
"It is absolutely fantastic to see Steve taking part, hopefully he will motivate others."
Lake Windermere is Britain's largest natural lake, with a length of 10.5 miles and depths of up to 220ft.
Fans of McFadden can sponsor his efforts by visiting the star's Justgiving fundraising page.