As a young man, Patterson had attended Greenville College for two years. After the study of law, he was admitted to the bar in 1841. He practiced law in Greeneville and also operated a manufacturing concern. He served as judge of the former 1st Circuit of Tennessee from 1854 to 1863.
A staunch Union supporter (as were most of his fellow East Tennesseans), he was elected by the Tennessee General Assembly to the U.S. Senate when Tennessee became the first state which had been part of the former Confederacy to be readmitted to the Union on July 24, 1866. He presented his credentials to the Senate on July 26, but they were challenged; he was not permitted to take the oath of office until July 28.
Patterson had married in 1855 Martha Johnson, daughter of former Tennessee Governor and Senator Andrew Johnson, who was President of the United States when Patterson won Johnson's previously held Senate seat. This placed Patterson in something of an awkward position when Johnson was impeached by the United States House of Representatives in February 1868. According to the U. S. Constitution, the Senate had the duty to try Johnson on the charges, and did so from March to May 1868, with the House impeachment managers failing to prove their case by a margin of one vote short of the constitutionally-imposed requirement of a two-thirds majority. (Patterson felt that his father-in-law was not guilty and that the charges against him were contrived, which has generally been the consensus of historians in the decades following the impeachment but not a sentiment shared universally.)
Patterson retired from public life when his Senate term expired on March 3, 1869, simultaneous with that of his father-in-law's as President. He returned to East Tennessee to manage his relatively vast agricultural interests. On November 3, 1891, Patterson died in the small community of Afton and was interred with the Johnson family in the Andrew Johnson National Cemetery in Greeneville.