The Senate voted on Thursday to approve the most sweeping overhaul of the nation's immigration system in a generation, sending a wide-ranging bill on to the House, where it faces a far less certain future.

By a vote of 68-32, the Senate approved the so-called Gang of Eight's massive reform bill, which would offer undocumented workers living in the U.S. with a pathway to citizenship, and impose tough new border security measures.

The centerpiece of the bill is a provision that would allow the estimated 11 million undocumented immigrants currently living in the U.S. to apply for citizenship after meeting certain benchmarks over a 13-year period. Citizenship applicants would need to pass background checks, pay back taxes and fees and, after 10 years, finally be available to apply for green cards. After three years with green cards, those immigrants could then become citizens.

The bill would also expand the number of temporary visas to high-skilled workers; update the nation's system for verifying workers' legal status; and double the number of border enforcement agents while building 700 miles of additional fencing along the U.S.-Mexico border.

It is the citizenship provision that proved most thorny in Senate discussions, and that could ultimately down the bill in the House. Many conservative members of Congress have balked outright at any bill that contains what they say amounts to amnesty for illegal immigrants.

Though the Republican Party conceded in a post-election autopsy report that it needed to better court minority voters, many party leaders have still resisted the immigration reform efforts on principle.

Sen. Marco Rubio (R-Fla.), the most visible member of the Gang of Eight, has sought to frame the citizenship provision as a conservative issue. Rubio, who is widely believed to be mulling a 2016 White House bid, has lobbied hard to get the bill passed, even as it on multiple occasions appeared destined for failure.

The bipartisan legislation, drafted over months by a coalition of four Republicans and four Democrats, represents a compromise between a wide array of interests. Business and labor leaders signed on early in support, as did immigration advocates and border hawks.

It was the addition of tougher border security provisions at the last minute, though, that was seen as the linchpin to garnering broad bipartisan support among lawmakers. Sen. Mark Kirk (R-Ill.), for one, said those additional provisions convinced him to back the bill.

However, while the Senate overwhelmingly passed the legislation, the House is another matter.

House Speaker John Boehner (R-Ohio) has said he won't bring the bill up for a vote unless it has the support of a majority of Republicans in that chamber. Whether those votes exist has yet to be seen.

Citing that uncertainty in remarks immediately before the vote, Sen. Patrick Leahy (D-Vt.) urged the House to act.

"This issue is far too important to ignore or to let it languish," he said. "We shouldn't play politics with an issue that is quintessentially American."