"Serious health issues have recently arisen in our family, and under the circumstances, I have decided to discontinue my campaign. My children and their futures were the motivation for our campaign and their health and well being will always be my overriding priority," Cheney said in a statement.
She did not offer specifics about the health issues impacting her family. Cheney and her husband, Phil Perry, have five children.
Cheney, 47, announced in July that she would challenge Sen. Mike Enzi in the Republican primary, a decision that seemed to catch the incumbent by surprise. What followed was a whirlwind six months that transformed the normally cordial Wyoming political landscape into a heated arena in which old bonds were frayed, tensions ran high and outside groups entered the mix.
Cheney's decision spares Enzi a top competitor in what was shaping up as the toughest test since his first election to the Senate in 1996.
Cheney sought to run to Enzi's right and got off to a fast fundraising start, bringing in more than $1 million from July to September, which was more than Enzi raised during that period. But she was hamstrung by distracting developments in her personal life that spilled into public view, most notably a feud over same-sex marriage with her younger sister Mary Cheney, who is a lesbian.
After Liz Cheney explained that she personally opposed same-sex marriage, Mary Cheney slammed her in public -- first in August and later in November, when Mary's wife, Heather Poe, also chimed in.
"Liz has been a guest in our home, has spent time and shared holidays with our children, and when Mary and I got married in 2012 -- she didn't hesitate to tell us how happy she was for us," Poe wrote on Facebook. "To have her now say she doesn't support our right to marry is offensive to say the least."
The contest attracted the attention of several outside conservative groups, atypical for a race in the sparsely populated state. Allies of Enzi had formed a super PAC, and national conservative groups ran television ads attacking both candidates in 2013, very early considering the primary won't take place until August 2014.
One such ad hit Liz Cheney from the right, casting her as insufficiently conservative on gay marriage because she did not support
oppose a constitutional amendment banning gay marriage. Another one from a separate group cast Enzi as insufficiently conservative in his opposition to the federal health-care law.
Liz Cheney also faced carpetbagging charges from critics. While her family has roots in Wyoming and she lived there as a child, she spent much of her adult life in Northern Virginia. She made a concerted effort illustrate her family's history in Wyoming; it was the focus of her campaign launch as well as her first television ad.
Separately, tension between Liz Cheney's mother and former senator Alan Simpson became a flash point in the campaign.
Limited early polling showed Enzi leading Liz Cheney by a wide margin, underscoring the challenge the first-time candidate faced. Cheney's father emerged as one of her most vocal advocates, vouching for her in media interviews. The former congressman and vice president had harsh words for Enzi on occasion, a striking posture considering that the two were never seen as rivals.
Liz Cheney's decision to leave the race likely puts Enzi in the driver's seat to secure another term. The 69-year-old hasn't drawn any other high-profile Republican challengers, and he is not viewed as a top target of the political right. Democrats, meanwhile, have yet to field a candidate for the race in the heavily conservative state.
In a statement Monday afternoon, Enzi said he and his wife respect Liz Cheney's decision.
"While it is not always easy, Diana and I have always believed in putting family first. We have tremendous respect for Liz’s decision. She and her entire family are in our thoughts and prayers," Enzi said. "I remain as committed as always to the job the people of Wyoming have elected me to do. I look forward to continuing my campaign for re-election in the coming months."
CNN first reported Liz Cheney's decision late Sunday.
In her statement Monday morning, Liz Cheney vowed to continue fighting for the issues she underscored in her campaign.
"Phil and I want to thank the thousands of people in Wyoming and all across the country who have supported my campaign," she said. "As a mother and a patriot, I know that the work of defending freedom and protecting liberty must continue for each generation. Though this campaign stops today, my commitment to keep fighting with you and your families for the fundamental values that have made this nation and Wyoming great will never stop."
Updated at 1:45 p.m.