At a rally at the state Capitol in Phoenix Tuesday, Brewer said expansion would bring in billions in federal dollars while saving the lives of people who otherwise would have no health coverage, The Arizona Republic reported.
While stating that "I've always been proud to be a member of a pro-life party," the governor said "I refuse to stand by and let this many people needlessly suffer, especially when we have a solution."
Brewer said without expansion 50,000 people would be dropped from Medicaid when a federal waiver expires at the end of the year.
Six GOP lawmakers, including House Health Committee Chairwoman Heather Crane, stood with Brewer at the rally.
Chris Herstam, a lobbyist and former GOP lawmaker, described the legislation as "very basic, easy to understand," and said it was a testament to Brewer's "political courage."
Grass-roots Republican officials are among the critics blasting the proposal. They argue the federal government can't afford to expand Medicaid and that expanding entitlements goes against GOP principles.
Republican legislators fear the federal government could reverse course on its willingness to pay for most of the expansion and stick the state with the additional Medicare costs.