This story has been updated.
Earlier this year: [Reid held first news conference, said he planned to run in 2016]
In an interview with The Washington Post, he said that he and his wife, Landra, had been contemplating retirement for many years, something he almost did back in 2010 when he won a grueling race for a fifth term. He spent the past few months recuperating so that he could announce his retirement without people suggesting that it was because of his health or his political standing back home.
Instead, Reid said, he had seen too many of his peers stay in the Senate long past their prime, tarnishing their legacies. He feared that another six-year term -- he would be 83 when it ended -- would overshadow the first "34 years" in Congress.
"I don't want to be a pinch hitter," Reid said from his home at the residences at Ritz Carlton in Washington's West End.
Reid suffered at least three broken ribs and broke several bones around his right eye in January while exercising at his suburban Las Vegas home.
After several weeks of recovery at home with his wife, Landra, Reid returned to the Senate earlier this year with a badly bruised face, wearing protective glasses over his right eye as doctors worked to bring back his vision. The bruises have dissipated, but the glasses remained.
The announcement, kept as a closely guarded secret, was carefully orchestrated. It began with filming a three-minute video announcing his decision, a lengthy written statement, and then interviews with The Washington Post, the New York Times, the Los Angeles Times and Las Vegas radio.
Reid quickly endorsed Sen. Charles E. Schumer (D-N.Y.) to succeed him as leader, suggesting that his potential rival for the post, Sen. Richard J. Durbin (D-Ill.), would stand down and let Schumer claim the post without opposition. Back home, Reid lined up his political machine to back the former state attorney general, Catherine Cortez Masto, for the Democratic nomination to run for his seat in what will become one of the most competitive Senate races in the nation.
Now minority leader after an eight-year run as majority leader, Reid returned in fighting form and held his caucus together on key showdowns with Republicans, including a battle over funding the Department of Homeland Security and Obama's executive actions on immigration.
In the interview, Reid acknowledged that he has had his share of disputes with Obama's White House but recognized that his legislative legacy in Washington is very intertwined with the president who will also retire at the end of 2016.
"He and I are gonna go out together," Reid said. The first two years of Obama's reign were "one of the most successful legislative times in history," he said, when the health law was enacted, the Dodd-Frank bill revamping Wall Street laws passed and a roughly $800 billion economic stimulus package won approval.
Weeks ago, Reid had assembled his entire staff and assured them that he would run for reelection. He had begun to hold fundraisers for his 2016 campaign and his Nevada-based advisers were assembling top aides to run his reelection bid, but he showed signs that he was considering retirement with a slower fundraising pace and a transition among his senior staff that was happening at a slow pace.
Last year, he sold his home in Searchlight, the Nevada mining town where he grew up and had built his dream home, and purchased a condo near Las Vegas so that he and his wife could be closer to their grandchildren.
Reid's Democratic colleagues praised the man who, deep in the minority with just 45 seats when he took over in 2005, led them to a super-majority of 60 seats in 2009 and helped pass sweeping laws that defined Obama's administration, before a brutal 2014 sent them back into the minority.
“Harry is one of the best human beings I've ever met," Schumer, the No. 3 Democratic leader, said in a statement. "His character and fundamental decency are at the core of why he’s been such a successful and beloved leader. He’s so respected by our caucus for his strength, his legislative acumen, his honesty and his determination."
"Harry Reid is one of the ablest leaders of the Senate Democratic caucus in modern history," Durbin said.
Republicans said Reid's decision showed that the Democratic hopes of winning the majority in 2016 were a stretch. "Senator Harry Reid has decided to hang up his rusty spurs. Not only does Reid instantly become irrelevant and a lame duck, his retirement signals that there is no hope for the Democrats to regain control of the Senate," Ward Baker, executive director of the National Republican Senatorial Committee, said in a statement.
Reid's life story almost seems to come from a different era, before billionaires with super PACs groomed polished candidates who were taught to never make a gaffe for fear that someone might be recording that moment. The son of a miner and a mother who washed clothes at a brothel, Reid took up boxing in his teenage years, channeling a temper into sport. Local businessmen helped pay for his college tuition at Utah State University, and, after getting accepted into George Washington University Law School, he worked his way through to a law degree by serving as a Capitol Police officer.
In Nevada, he slowly but surely climbed the ranks of local offices -- including a stint as gaming commissioner in which he was targeted by the mafia -- and in 1982 he won a seat in the U.S. House. In 1986, he won his seat in the Senate and has come out on top in a series of close races ever since.
The consummate insider, Reid took all the tough jobs that many colleagues never would accept, earning their credit and praise and rising up the leadership ranks. Faced with another tough reelection -- one in which his health was questioned -- Reid decided to retire and allow the full resources of Senate Democrats to go to the next generation of candidates.
Famous for his sharp tongue, critics called Reid's most heated statements "gaffes," but they missed the broader point: He meant most of his insults and often was proud of them. He once called Supreme Court Justice Clarence Thomas an "embarrassment" and said then-President George W. Bush was a "liar" and later a "loser" in front of a high school class in Las Vegas.
He apologized later for calling him a loser -- Bush was traveling abroad at the time -- but took pride in never apologizing for the 2002 "liar" remark.
Reid said he would not build a library, that he had no plans for raising money for a political institute at a university in his name. He's not certain what he will do next, other than battling for his final 21 months in office to get Democrats back into the majority in 2017.
"We all find other fights," he said.