Thomas Martin Easterly (October 3, 1809 – March 12, 1882) was a 19th-century American daguerreotypist and photographer. One of the more prominent and well-known daguerreotypists in the Midwest United States during the 1850s.

Born in Guilford, Vermont, he was the second of five children born to Tunis Easterly and Philomena Richardson. He reportedly came from a poor background, his father being a farmer and part-time shoemaker, and was living away from home at age 11. Around 1830, he was living in St. Lawrence County, New York although little is known of his early years. He began practicing photography in 1844 taking outdoor photographs of architectural landmarks and scenic sites in Vermont. He was also the first and only daguerreotypist to identify his work using engraved signatures and descriptive captions.

In the fall of 1845, Easterly traveled to the Midwest United States and toured the Mississippi River with Frederick F. Webb as representatives of the Daguerreotype Art Union. The two gained some notoriety from their photography of the criminals convicted of the murder of George Davenport in October of that year. The following spring, Easterly and Webb went their separate ways with Easterly traveling on his own to St. Louis. He soon became popular for his portraits of prominent residents and visiting celebrities which were displayed in a temporary gallery on Glasgow Row. One of these portraits was that of Chief Keokuk taken March 1847. He also took a daguerreotype of a lightning bolt, one of the first recorded "instantaneous" photographic images, while in St. Louis. The only known photograph of the first St. Charles Hotel in New Orleans, built to be the world’s finest, was taken by Easterly ca. 1847.

Easterly was brought back to Missouri by John Ostrander, founder of the first daguerreotype gallery in St. Louis, in early 1848. Preparing for an extended "tour of the south", Ostringer asked Easterly to manage his portrait gallery. Easterly would continue running the gallery when Ostringer died a short time later. In June 1850, he married schoolteacher Anna Miriam Bailey and settled in St. Louis permanently.

During the 1860s, improvements in photographic development caused daguerreotypes to become out of fashion. Easterly refused to acknowledge these changes believing the highly detailed daguerreotypes were far superior in terms of beauty or permanence urging the public to "save your old daguerreotypes for you will never see their like again". During the next decade, both his health and financial situation worsened. Despite the declining interest for pictures on silver, he was able to maintain his gallery until it burned in a fire in 1865. He was forced to move to a smaller location and continued working in near obscurity until his death in St. Louis on March 12, 1882. He had suffered from a long illness and partial paralysis in his final years and is thought to have been caused by prolonged exposure to mercury, one of the key ingredients used in the daguerreotype process. After his death, his wife sold most of his personal collection to John Scholton, another noted St. Louis photographer. The Scholton family eventually donated the plates to the Missouri Historical Society where they remained for nearly a century before being rediscovered during the 1980s by art scholars studying pre-American Civil War photography.