Congressional Republicans unveiled the most sweeping overhaul of the nation’s tax code in three decades Friday evening with an eye toward final passage next week after two key GOP senators endorsed the legislation.

"This is happening. Tax reform under Republican control of Washington is happening," House Speaker Paul Ryan, R-Wis., told rank-and-file members in a conference call. "Most critics out there didn't think it could happen. ... And now we're on the doorstep of something truly historic."

The final version of the so-called Tax Cuts and Jobs Act keeps seven tax brackets, but reduces rates for five of them. The new rates start at 10 percent and rise to 12, 22, 24, 32, 35 and 37 percent. The corporate tax rate is reduced from 35 percent to 21 percent and the bill provides sweeping tax deductions to other businesses, lowering their top effective tax rate to about 30 percent instead of 39.6 percent.

The standard deduction -- used by around two-thirds of households -- would be nearly doubled to $12,000 for individuals and $24,000 for married couples. But deductions for state and local taxes are scaled back, allowing families to deduct only up to a total of $10,000 in property and income taxes. The deduction is especially important to residents of high-tax states such as New York, New Jersey and California.

The final package would also double the basic per-child tax credit for families making up to $400,000 a year from $1,000 to $2,000. Sen. Marco Rubio, R-Fla., was expected to vote for the bill after winning a late concession that would make up to $1,400 of the credit available as a tax refund to lower- and middle-income families with relatively small tax bills.

Another GOP holdout, Bob Corker of Tennessee, said Friday that he would endorse the bill, describing it as an opportunity "to make U.S. businesses domestically more productive and internationally more competitive [and] one we should not miss."

"I realize this is a bet on our country's enterprising spirit,” Corker added, "and that is a bet I am willing to make."

Senate Republicans passed their original tax bill by a vote of 51-49 — with Rubio's support. Corker was the only Republican to vote against the original bill out of concerns about its effect on the federal deficit.

Republicans, who hold a 52-48 majority in the Senate, can only afford to lose two votes before the bill is defeated. Vice President Mike Pence would have to break a tie if required.

The House is expected to vote on the final bill Tuesday, with a Senate vote to follow later in the week. Sen. John McCain, R-Ariz., is at a Washington-area military hospital being treated for the side effects of brain cancer treatment, and Sen. Thad Cochran, R-Miss., had a non-melanoma lesion removed from his nose earlier this week. GOP leaders are hopeful they will be available next week.

The White House said Trump "looks forward to fulfilling the promise he made to the American people to give them a tax cut by the end of the year."

Republicans have promised the bill would provide needed tax relief to Americans at all income levels.

"Americans deserve a new tax code for a new era of American prosperity," House Ways and Means Committee Chairman Rep. Kevin Brady, R-Texas, said Friday. "I'm very excited about this moment. It has been 31 years in the making ... Everyone's life will be better off under tax reform."

Democrats disagree, arguing that the legislation would help wealthy Americans and big business at the expense of the poor and middle class.

"Under this bill the working class, middle class and upper middle class get skewered while the rich and wealthy corporations make out like bandits," Senate Minority Leader Chuck Schumer, D-N.Y., said in a statement. "It is just the opposite of what America needs, and Republicans will rue the day they pass this."

Business owners who report business income on their personal tax returns would be able to deduct 20 percent of that income.

The agreement also calls for repealing ObamaCare's individual mandate, a major step toward the ultimate GOP goal of unraveling the law. It retains a deduction for medical expenses and an exemption for graduate school tuition waivers.

The business tax cuts would be permanent, but reductions for individuals would expire in 2026 — saving money to comply with Senate budget rules. In all, the bill would cut taxes by about $1.5 trillion over the next 10 years, adding billions to the nation's mounting debt.

The legislation also contains a provision that would open Alaska's Arctic National Wildlife Refuge to oil and gas drilling, a longtime Republican priority that is fiercely opposed by Democrats and environmental groups.

Sen. Lisa Murkowski, R-Ak., and other Republicans say drilling in the 19.6-million-acre refuge can be done safely with new technology, while ensuring a steady energy supply for West Coast refineries.

Fox News' Chad Pergram and The Associated Press contributed to this report.