Thomas Williams was born in Greensburg, Pennsylvania on 28th August, 1806. He graduated from Dickinson College in 1825 and was admitted to the bar three years later. Williams worked as a lawyer in Greensburg (1828-32) before moving to Pittsburgh in 1832. He joined the Whig Party and edited its political magazine, The Advocate.
A member of the Republican Party, Williams was elected to the 38th Congress and took his seat in March, 1863. Williams was one of the seven members chosen by the House of Representatives to prosecute its impeachment charges against President Andrew Johnson.
Williams did not share the views of the dominant Radical Republicans in Congress and decided to retire in 1868. Williams lived in Allegheny City, Pennsylvania, until his death on 16th June, 1872.