Paul told a Texas news organization, The Facts, that he decided to make the announcement early to give potential candidates for his seat time to make plans.
"I felt it was better that I concentrate on one election," Paul said. "It's about that time when I should change tactics."
Paul, who turns 76 next month, is in his 12th term in Congress, representing the 14th District, a swathe of the Gulf Coast southwest of Houston that includes the city of Galveston. A Pennsylvania native, he moved to Texas and practiced obstetrics in Lake Jackson after serving in the U.S. Air Force as a flight surgeon.
During his time in Congress, he has become known as a libertarian willing to take on most of the Republican Party, especially in foreign affairs. In 2008, his presidential campaign attracted enthusiastic volunteers but few delegates.
Paul's son and political heir, Rand, is now the junior senator from Kentucky.