Marcus Junius Parrott was born on October 29, 1828 in Hamburg, South Carolina, the son of a wealthy Quaker family. His parents left the South when he was a young boy and he grew up in Dayton, Ohio. He was prepared at the Dayton Academy, and went on to study at Ohio Wesleyan University. In December, 1847, Parrott was expelled from Ohio Wesleyan over a clash with his Greek instructor and his refusal to sign a pledge to respect that faculty member. He went on to spend his junior and senior years at Dickinson College in Carlsile, Pennsylvania where he was an active member in the Belles Lettres Society and was co-editor -- with Moncure Conway and John J. Jacob, the future governor of West Virginia -- of the pioneering student publication, the Collegian. Parrott graduated with his class in May, 1849 and moved to Boston, Massachusetts to attend the Cambridge Law School for two years. During his law school career Parrott attended many lectures at Faneuil Hall given by noted abolitionists such as Charles Sumner, George Thompson, William Lloyd Garrison, Wendell Phillips, Theodore Parker, and Frederick Douglas.

After law school, Parrott moved back to Dayton and practiced law for several years before serving as a Democrat in the Ohio Legislature from 1853 to 1854. Parrott's interest in the free-state and abolitionist cause prompted him to move to Leavenworth, Kansas in 1855, where he became a Kansas Supreme Court reporter and a representative to the Topeka Consitutional Convention that October. By this time an enthusiastic member of the Free-State Party and optimistic for the realization of a slave-free Kansas, Parrott served as a delegate to Congress for the Kansas Territory from 1857-1861. He was in Washington when Kansas was finally granted statehood in January 1861 as a free state and it was he who telegraphed the news to waiting Kansans. Parrott ran as one of the new U.S. Senators for the state but achieved only a narrow third. He failed similarly to win a House of Representatives seat as an Independent in 1862 and as a Democrat in 1874.

In the late 1860's Parrott retired to a farm outside Leavenworth with his wife and three children. His failing health prompted him to make a trip back to Ohio in 1877 to visit his relatives. After suffering from several strokes and paralysis, Parrott died there on October 4, 1879 at the age of fifty. He was buried in the Woodlawn Cemetery in Dayton.