Lemuel Todd was born in Carlisle, Pennsylvania on July 29, 1817. He entered the class of 1839 at Dickinson College in his home town, took the classical course, and was elected to the Union Philosophical Society. Upon graduation, he studied law in the offices of General Samuel Alexander, an earlier Dickinson graduate, and, when he was called to the Cumberland County bar in 1841, took up a partnership with Alexander and began a practice in Carlisle.
Todd's reputation grew and, in 1854, he ran for the United States Congress as a Republican and was elected. He sat from early 1855 to early 1857 but failed in his reelection bid of 1856 in a district that was by that time largely Democratic. He returned to his legal work in Carlisle until April 1861, when he raised a company of volunteers in the county at the outbreak of the Civil War. This unit was accepted for three years service in June of 1861 and became Company I of the First Reserve, 30th Pennsylvania Volunteer Infantry. He was promoted to Major and third in command of the unit. He fought with the 30th in a series of engagements including Gaines Mill, Second Bull Run, and South Mountain, briefly taking command of the unit at one point. Severe attacks of illness in the summer of 1862 saw him withdraw from the regiment on September 15, 1862. In the winter of 1862-63 he organized the influx of drafted men in the eastern half of the state at Philadelphia and Governor Curtin appointed him as Inspector General of state troops on the governor's staff and was therefore responsible for militia and State Guard units, especially during the "emergency" that Lee's summer 1863 invasion brought on. Following the war, Todd returned to practice in Carlisle. He was again elected to Congress from the district as a Republican in 1872 and served one term between 1873 and 1875, declining renomination.
In 1849 Todd married Sarah Anna Watson of Adams County and the couple had several children, one of whom, Edward, attended Dickinson. Lemuel Todd practiced law until his death on May 12, 1891. He was seventy-three years old.