The change comes as "Good Morning America" tries to shore up sinking ratings at a time of tighter competition with NBC's "Today" show and reflects the importance of the show to parent Walt Disney Co.'s bottom line.
Strahan has worked a couple of days a week at "GMA" for the past two years, but he always has to leave midway through to head to the "Live with Kelly and Michael" studio on Manhattan's upper West Side. He's joining the show's regular cast of Robin Roberts, George Stephanopoulos, Lara Logan, Amy Robach and Ginger Zee.
Starting in September, he'll be there five days a week for the full two-hour show.
The former New York Giant was selected in 2012 to replace Regis Philbin as Ripa's co-host on the talk show, which airs directly after "Good Morning America" at 9 a.m. in most markets.
"Michael's proven to be a tireless and versatile broadcaster with an incredible ability to connect with people, from veterans and all kinds of newsmakers to a host of American cultural icons," said ABC News President James Goldston. "He is a great modern thinker and leader."
"Good Morning America" remains television's most popular morning show, averaging 4.96 million viewers a day since the beginning of the year. But that audience is down 10 percent from 2015, according to the Nielsen company.
More importantly, "GMA" is down 15 percent among viewers aged 25-to-54, and that's the demographic that most advertising rates for news programs are based upon. NBC now leads ABC in this category for 2016.
Given a choice of trying to help one show while simultaneously hurting another, it was no contest: Disney has much more money at stake with "Good Morning America" than with "Live with Kelly and Michael."
ABC said Tuesday that a search for Strahan's replacement as Ripa's partner will begin in the fall. "Live" is a solid performer in the ratings, and was a close second to "Dr. Phil" among daytime syndicated shows in the most recent ratings report. Ripa and Strahan shared an Emmy for outstanding entertainment talk show hosts last year.
"The combination has been great for the show," said Bill Carroll, an expert in the syndication market for Katz Media. "Michael has brought a new audience to the show and a great energy working with Kelly."
The show's chief advantage in searching for a replacement is longtime producer Michael Gelman, who dates back to the show's formative years with Philbin and Kathie Lee Gifford, he said. The show has commitments to be on the air at least through 2020.
Strahan, who retired from the NFL in 2008 following a 15-year playing career, will remain as a co-host of "NFL on Fox" on the weekends.