Foxx said she enjoys her job in the House and advised any candidate who enters the race to focus on ending ObamaCare and reducing the national debt.
Hagan is seen as a top target in 2014, as one of a handful of Democrats running for reelection in a Republican-leaning state won by Mitt Romney in 2012.
In a Democratic affiliated Public Policy Poll released earlier this month, Foxx had been favored by Republicans to get into the race. However, observers did not expect her to jump in.
North Carolina state House Speaker Thom Tillis (R) is seen as the front-runner of the Republican nomination but trails Hagan in the polls.
The PPP poll earlier this month found that a series of conservative measures passed through the state legislature have dragged down the poll numbers of Tillis and other potential Republican candidates.