Updated 11:30 p.m. | Oklahoma GOP Sen. Tom Coburn plans to leave the Senate early and will resign his seat at the end of the current Congress.

Coburn had already pledged not to seek another term in the Senate come 2016, but his announcement Thursday will open the seat ahead of schedule. Coburn is waging a fourth battle with cancer, and people in the state have been aware that Coburn might give up the seat ahead of schedule. Oklahoma will need to hold a special election to fill the seat.

“This decision isn’t about my health, my prognosis or even my hopes and desires. My commitment to the people of Oklahoma has always been that I would serve no more than two terms. Our founders saw public service and politics as a calling rather than a career,” Coburn said in a statement. “That’s how I saw it when I first ran for office in 1994, and that’s how I still see it today. I believe it’s important to live under the laws I helped write, and even those I fought hard to block.”

Coburn has been a crusader against what he views as wasteful government spending, publishing an annual “Wastebook” of programs he views as particularly outrageous. Notably, Coburn’s early retirement announcement came on the same day the Senate passed a $1.1 trillion omnibus appropriations bill.

However, Coburn did not cast a vote on that measure Thursday.

He serves as the ranking member on the Homeland Security and Governmental Affairs Committee. Before arriving in the Senate, he served in the House from 1995 to 2001.

Senate Minority Leader Mitch McConnell was among the first to issue a statement praising Coburn’s work, calling him “a legend in his own time.”

“No one has done more to awaken Americans to the threat posed by a government that chronically spends more than it takes in, and no one has worked harder at finding a solution. Today’s announcement is one that we all knew might come but that we all hoped wouldn’t. Fortunately, Tom has decided to stay with us throughout the year, so we will have the benefit of his wisdom and his counsel in the months ahead,” the Kentucky Republican said. “But I know I speak for all my Senate colleagues when I say that we’ll need that long to get used to the idea of losing Tom Coburn’s singular voice in our conference.”

Over the years, Coburn has had some great sparring matches with both Democrats and Republicans. His opposition to a 2009 public lands package led to the bill being nicknamed a “Tomnibus.” More recently, Coburn was among the chief opponents of a strategy favored by some fellow Republicans that tied funding the government to defunding Obamacare.

Coburn announced his retirement in a statement issued Thursday evening:

“Serving as Oklahoma’s senator has been, and continues to be, one of the great privileges and blessings of my life. But, after much prayer and consideration, I have decided that I will leave my Senate seat at the end of this Congress.

“Carolyn and I have been touched by the encouragement we’ve received from people across the state regarding my latest battle against cancer. But this decision isn’t about my health, my prognosis or even my hopes and desires. My commitment to the people of Oklahoma has always been that I would serve no more than two terms. Our founders saw public service and politics as a calling rather than a career. That’s how I saw it when I first ran for office in 1994, and that’s how I still see it today. I believe it’s important to live under the laws I helped write, and even those I fought hard to block.

“As a citizen legislator, I am first and foremost a citizen who cares deeply about the kind of country we leave our children and grandchildren. As I have traveled across Oklahoma and our nation these past nine years, I have yet to meet a parent or grandparent who wouldn’t do anything within their power to secure the future for the next generation. That’s why I initially ran for office in 1994 and re-entered politics in 2004. I’m encouraged there are thousands of Americans with real-world experience and good judgment who feel just like I do. As dysfunctional as Washington is these days, change is still possible when ‘We the People’ get engaged, run for office themselves or make their voices heard. After all, how else could a country doctor from Muskogee with no political experience make it to Washington?

“As a citizen, I am now convinced that I can best serve my own children and grandchildren by shifting my focus elsewhere. In the meantime, I look forward to finishing this year strong. I intend to continue our fight for Oklahoma, and will do everything in my power to force the Senate to re-embrace its heritage of debate, deliberation and consensus as we face our many challenges ahead.

“My God bless you, our state and our country.”