Lifestyle anchor since returning to the show in 2011, Spencer now has billing parity with Robin Roberts and George Stephanopoulos.
She was the show's national correspondent from 1999 to 2004. Then, for seven years, she was a host of "The Insider."
Her promotion comes as "GMA" continues to beat NBC's "Today" show in the ratings, but after it recently lost two members of its team: Sam Champion and Josh Elliott.
The other current members of the "GMA" family are Amy Robach and Ginger Zee.
This week, "GMA" welcomed Michael Strahan, a co-host of the daily "Live with Kelly and Michael," as a contributor.