Roberts, 46, revealed her diagnosis to viewers Tuesday. She said doctors believed they had caught the cancer early.
An ABC News spokeswoman said Roberts' mother and sisters traveled from the Mississippi Gulf Coast and New Orleans to be with her for the surgery. Roberts has said she has no family history of breast cancer.
She has been an anchor at "GMA" since 2005, and had been a newsreader for the program.
When she made the announcement, Roberts said: "I am so blessed that I found this in the early stages and the prognosis is so promising that my doctor expects me to be flying planes and hanging on to submarines in the middle of the Atlantic and scaling the Mayan pyramids in no time."
Roberts, who is co-anchor of "Good Morning America" with Diane Sawyer, said she examined herself and found a lump on her breast the same day she had done a report on former "GMA" movie critic Joel Siegel, who died of colon cancer last month.
Roberts, who is single, said there is no history in her family of breast cancer.