By Alex Dobuzinskis
Hagan struggled with encephalitis or brain inflammation for about three years after suffering a tick bite. She died sleeping at her home in Greensboro, North Carolina, according to the Charlotte Observer.
"We are heartbroken to share that Kay left us unexpectedly this morning," his family told the newspaper.
Prior to running for the US Senate, Hagan worked in the banking industry and served in the North Carolina state Senate.
Hagan defeated Republican Senator Elizabeth Dole in the 2008 elections, in which Democratic presidential candidate Barack Obama defeated the southern state in a reversal of years of losses by Democrats in the country. Dole, a former cabinet secretary, is the wife of former US Senator and 1996 nominee for the Republican presidency, Bob Dole.
Hagan has served on several Senate committees, including the Armed Services Committee. His father and brother were in the US Navy.
In 2010, she joined other Democrats in the vote for the Affordable Care Act, popularly known as Obamacare, which became Obama's signature domestic law.
In the same year, Hagan became one of only five Democrats in the Senate to vote against a bill to allow immigrants to enter the United States as unauthorized children to remain legally in the country. The project, known as the DREAM Act, was defeated.
Hagan narrowly lost to Thom Tillis, the Republican Speaker of the North Carolina House of Representatives, in the 2014 elections.
Tillis, in a Twitter statement, said he and his wife, Susan, were "absolutely heartbroken over Senator Kay Hagan's sudden death."
Obama said in a statement that Hagan is a fantastic "civil servant", eager to find common ground, willing to overcome the partisan fight and always focused on making progress for the people he served. "
Former Vice President Joe Biden, a leading Democratic candidate for the party's nomination to face Republican President Donald Trump in the 2020 elections, said in a statement that he saw Hagan and her husband, Chip, during a parade in Durham, Carolina. North on Sunday. He called Hagan a crucial ally in the Obama administration's battle to pass the Affordable Assistance Act.
The story goes on
(Reporting by Alex Dobuzinskis in Los Angeles)