United States Senator. Only individual to represent three different states in Senate. Attended hedge school and private schools in Ireland and pursued classical studies. Fluent in four languages. Immigrated to US, 1826. Taught school in Illinois. Studied law, admitted to bar, commenced practice in Kaskaskia, Randolph County, Illinois, 1832. Militia member, Black Hawk War, 1836. Member, Illinois House, 1836. State Auditor, 1839. Nearly fought duel with Abraham Lincoln, 1842. Anonymously written attacks on Democrat Shields appeared in Illinois papers and he believed Whig Lincoln the author, though actual author was likely Lincoln's future wife Mary Todd. Shields demanded satisfaction of a duel. Seconds convinced parties not to fight after Lincoln denied authorship and Shields accepted explanation. Shields and Lincoln became friendly after settling dispute. Judge, Illinois Supreme Court, 1843. Commissioner, US General Land Office 1845 to 1847. Served during Mexican War, commissioned Brigadier General of Volunteers, 1846 Brevetted Major General, 1847. Commanded brigade at battles of Vera Cruz and Cerro Gordo, where he was wounded. Returned to service and fought at Contreras and Churubusco. Wounded again at Chapultepec. Appointed Governor, Oregon Territory, serving 1848-49. Elected by Illinois legislature to US Senate for term commencing March 4, 1849. Declared ineligible to hold seat on grounds that since his naturalization documents had been filed eight and a half years previously he did not meet nine-year citizenship requirement specified by Constitution. Elected again by special session of state legislature for same term and took seat six months later, serving October 27, 1849 to March 3, 1855. Chairman, Committee on District of Columbia, Committee on Military Affairs. Editor "A History of Illinois, from its Commencement as a State in 1818 to 1847," 1854. Moved to Minnesota, 1855. Upon Minnesota's admission to Union elected to US Senate, serving May 11, 1858 to March 3, 1859. Chairman, Committee on Revolutionary Claims. Moved to California, employed as superintendent of a mine. Married Mary Ann Carr. Five children, three of whom survived to adulthood. Served in Union Army as Brigadier General, 1861 to 1863. Defeated forces under command of Thomas "Stonewall" Jackson at Battle of Kernstown, where he was again wounded, 1862. Resigned from service after military abilities were questioned during consideration of his promotion to Major General. Returned to California. Later moved to Carrollton, Missouri. Missouri House, 1874. Missouri Adjutant General, 1874 to 1877. Missouri House, 1879. Missouri Railroad Commissioner. Elected to US Senate to fill vacancy caused by death of Lewis V. Bogy, serving January 27, 1879 to March 3, 1879. Declined renomination because of failing health. Died while delivering speech on lecture tour. Represents Illinois in US Capitol's National Statuary Hall.