As a young man, Cockrell went to California in 1849 during the Gold Rush. He worked as a miner and a merchant near the Bear River. Cockrell returned to Missouri in 1853, where he engaged in agricultural pursuits, studied law and, for a time, was a minister in the Methodist Church.
Marriage and family
On April 7, 1852, he married Maranda "Jane" Douglas. They had five children together.
At the close of the war, Cockrell settled with his family in Sherman, Texas, where he practiced law. He was appointed as Chief Justice of Grayson County, Texas, in 1872. He served as delegate to the Democratic state conventions in 1878 and 1880.
He and his family moved from the northern area to Jones County, in the center of Texas. There he was appointed judge of the Thirty-ninth judicial district court in 1885. He was elected to the position in 1886 and re-elected in 1890.
In 1892, Cockrell was elected as a Democrat to the U.S. Congress, where he served until 1897. He was not a candidate for renomination in 1896. He returned to engage in farming and stock raising in Jones County.