Logan did not have any schooling until the age of 14. He then studied for 3 years at Shiloh College, served in the Mexican War as a lieutenant of volunteers. After the war, he studied law in the office of an uncle, graduated from the Law Department of Louisville University in 1851, and successfully practised law.
Logan entered politics as a Douglas Democrat, was elected county clerk in 1849, served in the State House of Representatives from 1853-54 and in 1857. For a time, during the interval, he was prosecuting attorney of the 3rd Judicial District of Illinois. In 1858 and in 1860, he was elected as a Democrat to the National House of Representatives. His loyalty to the Union raised speculation through the seccession winter of 1861-62. His family had migrated from the South, and he was best known for sponsership of harsh laws barring free blacks from the state and vehement defense of the Fugitive Slave Act. His name had been used to promote Confederate recruiting in his district in the southern tip of Illinois, and his brother-in-law had enlisted in the Confederate army. It was believed by many that he was a Southern sympathizer.
Though unattached and unenlisted, Logan fought at the 1st Bull Run, with a Michigan regiment. He returned to Washington, resigned his congressional seat in the spring of 1861, and entered the Union army as Colonel of the 31st Illinois Volunteers, which he organized. His regiment joined Lieutenant Gen. Ulysses S. Grant's army in Cairo, and fought with distinction at Belmont and Fort Donelsonn, where he was wounded leading his regiment. He was commissioned a Brigadier General afterwards and was regarded as one of the most able officers to enter the army from civilian life.
In Grant's campaigns, Logan's Division, the 3rd Division/XVII Corps, was the first to enter the city of Vicksburg in 1863, and after its surrender, he served as its military governor. He also received the Medal of Honor for his actions in the Vicksburg Campaign. He rose to the rank of major general of volunteers in November 1862, and in November 1863, he succeeded Major Gen. William T. Sherman to command the XV Army Corps.
After resigning from the army on August 17, 1865, Logan resumed his political career as a Republican, and was a member of the National House of Representatives from 1867-71, and a member of the U.S. Senate from 1871-77. He was elected again in 1879 and served until his death in 1886.
Logan was always a violent partisan, and was identified with the radical wing of the Republican Party. In 1868, he was one of the managers in the impeachment of President Andrew Johnson. He was one of the organizers of the Grand Army of the Republic and was its president different 3 times.
His war record and his great personal following contributed to his nomination for Vice-President in 1884 on the ticket with James G. Blaine, but he was not elected.
For this campaign, he commissioned the painting of the Atlanta Cyclorama which emphasized his heroism in the Battle of Atlanta. He urged the observance of Memorial Day, and he may have been the inventor of the idea. He was the author of "The Great Conspiracy: Its Origin and History" in 1886, a partisan account of the Civil War, and of "The Volunteer Soldier of America" in 1887.
Colonel - September 18, 1861
Brigadier General USV- March 21, 1862
Major General USV- November 29, 1862
1st Brigade, 1st Division, Army of the Tennessee (April 19-July, 1862)
1st Brigade, 1st Division, District of Jackson (July- September, 1862)
District of Jackson (September, 1862)
3rd Division, Right Wing, XIII Corps, Army of the Tennessee (November 1- December 18, 1862)
3rd Division, XVII Corps (December 18, 1862- July 20, 1863 and September- November 17, 1863)
XV Corps (December 11, 1863- July 22, 1864 and July 27- September 23, 1864 and January 8- May 23, 1865)