Gilmore was born in New Orleans, Louisiana. He was instructed by private tutors, graduating from the Central High School of New Orleans in 1874, from Seton Hall College, South Orange, New Jersey, in 1877, and from the law department of the University of Louisiana (now Tulane University) at New Orleans in 1879. He was admitted to the bar in 1880 and commenced practice in New Orleans, Louisiana. From 1888 to 1896, Gilmore served as assistant city attorney. He was city attorney from 1896 until March 15, 1909, when he resigned. He served as delegate to the Democratic National Convention in 1908.
Gilmore was elected as a Democrat to the Sixty-first Congress to fill the vacancy caused by the death of Robert C. Davey and served from March 30, 1909, until his death in Abita Springs, Louisiana, on July 18, 1910. He was interred in Metairie Cemetery, New Orleans, Louisiana.
His daughter, Martha Gilmore Robinson, was a women's rights and civic activist. His son, Samuel Louis Gilmore, Jr., was a poet and playwright, as well as an associate editor for The Double Dealer (magazine).
- "Martha Gilmore Robinson". KnowLA: Encyclopedia of Louisiana. Archived from the original on 2017-01-18. Retrieved 2016-09-16.
- "Samuel Louis Gilmore, Jr. Collection Finding Aid" (PDF). Special Collections & Archives, J. Edgar & Louise S. Monroe Library, Loyola University New Orleans. Retrieved 17 July 2018.
- United States Congress. "Samuel Louis Gilmore (id: G000223)". Biographical Directory of the United States Congress.
- Samuel Louis Gilmore, late a representative from Louisiana, Memorial addresses delivered in the House of Representatives and Senate frontispiece 1911
|U.S. House of Representatives|
Robert C. Davey
| Member of the U.S. House of Representatives
from Louisiana's 2nd congressional district
H. Garland Dupré