Dallas was born in Philadelphia and graduated from the College of New Jersey (now Princeton University) in 1810. He was admitted to the bar in 1813 and served as private secretary to Albert Gallatin, Minister to Russia. Dallas returned in 1814 and practiced law in New York City. He was solicitor of the Second Bank of the United States from 1816 to 1817.
Dallas returned to Philadelphia and was appointed deputy attorney general in 1817. He was mayor of Philadelphia from October 21, 1828, to April 15, 1829, then served as United States Attorney for the eastern district of Pennsylvania from 1829 to 1831.
He was elected as a Democrat to the United States Senate to fill the vacancy caused by the resignation of Isaac D. Barnard. Dallas served less than 15 months — from December 13, 1831, to March 4, 1833 — and declined to be a candidate for reelection. He was chairman of the Committee on Naval Affairs.
Dallas resumed the practice of law, was attorney general of Pennsylvania from 1833 to 1835, and served as the Grand Master of Freemasons in Pennsylvania in 1835 He was appointed by President Martin Van Buren as Envoy Extraordinary and Minister Plenipotentiary to Russia from 1837 to 1839, when he was recalled at his own request. Dallas was elected Vice President of the United States on the Democratic ticket in 1844 with James K. Polk and served from March 4, 1845 to March 4, 1849.
President Franklin Pierce appointed Dallas in 1856 as Envoy Extraordinary and Minister Plenipotentiary to Britain, where he served until 1861, when he returned to Philadelphia. He died there in 1864 at the age of 72 and was interred in St. Peter's Churchyard. Dallas County, Iowa and Dallas County, Texas, and several U. S. cities and towns elsewhere were named in his honor such as Dallas, Georgia, Dallastown, Pennsylvania and Dallas, Oregon the county seat of Polk County, Oregon. (It is debated that the city of Dallas, Texas, is named after the Vice President. Click here for more information)
Dallas was the son of U.S. Treasury Secretary Alexander J. Dallas and is the great-great-granduncle of former U.S. Senator Claiborne Pell of Rhode Island. He was also the brother of Naval officer Alexander J. Dallas and the uncle of George M. Bache and Alexander Dallas Bache. He was of Scottish heritage.