Sen. John McCain, R-Ariz., who thwarted the GOP's Obamacare repeal effort last summer, announced Thursday he is all in on the GOP tax legislation.

“After careful thought and consideration, I have decided to support the Senate tax reform bill. I believe this legislation, though far from perfect, would enhance American competitiveness, boost the economy, and provide long overdue tax relief for middle class families," McCain said in a statement.

“For too long, hardworking people in Arizona and around the country have not seen a raise in their paychecks. This bill would directly benefit all Americans, allowing them to keep a higher percentage of what they earn," he added. "According to the non-partisan Joint Committee on Taxation, every income bracket would see tax relief under this bill. The child tax credit would be doubled to $2,000 per child and the tax code would be substantially simplified."

The Senate is expected to take a final vote on tax reform either late Thursday night or Friday, Majority Leader Mitch McConnell said Thursday morning.

McCain has long been seen as a potential holdout on the bill.

The senior senator from Arizona tanked the GOP's push to reform the Affordable Care Act during the summer over complaints about how the bill was formed and the process it went through in the Senate. He called for a return to regular order and committee hearings on healthcare reform and other major bills.

While the Senate's tax reform package has gone through the committee process, there have been a number of complaints from critics about the formation process. McCain brushed those aside in his statement even though a major reform to the healthcare system is included in the package.

"For months, I have called for a return to regular order, and I am pleased that this important bill was considered through the normal legislative processes, with several hearings and a thorough mark-up in the Senate Finance Committee during which more than 350 amendments were filed and 69 received a vote," he said.

"I have also argued that health care reform, which is important both to the well-being of our citizens and to the vitality of our economy, should proceed by regular order. This bill does not change that. As a matter of principle, I’ve always supported individual liberty and believe the federal government should not penalize Americans who cannot afford to purchase expensive health insurance. By repealing the individual mandate, this bill would eliminate an onerous tax that especially harms those from low-income brackets. In my home state of Arizona, 80 percent of people who currently pay the individual mandate penalty earn less than $50,000 per year."

McCain also brushed aside concerns about how the bill would impact the deficit.

“I take seriously the concerns some of my Senate colleagues have raised about the impact of this bill on the deficit. However, it’s clear this bill’s net effect on our economy would be positive. This is not a perfect bill, but it is one that would deliver much-needed reform to our tax code, grow the economy, and help Americans keep more of their hard-earned money," he said.

“By lowering our high corporate tax rate to 20 percent, the bill would make our markets far more attractive for investment. It would also encourage American companies to repatriate assets now held overseas. Small businesses, which are vitally important to the dynamism of our economy, would also receive essential tax relief. Combined, these commonsense steps would promote economic growth and stimulate job creation here at home," he added.