In 1872, Aldrich became a partner in a banking enterprise in Selma, Alabama. While in the region, he investigated the existing coal-mining operations at Montevallo and around the Cahaba coalfield. The next year he secured a lease on the Montevallo coal mines and set to work extracting coal that summer. He purchased the mines outright in 1875 and named the surrounding settlement Aldrich, leasing the operation to his younger brother William while he prospected for new seams. He incorporated the Jefferson Coal Company in the town of Morris, from which he supplied fuel for the first successful coke-fired furnace in the Birmingham District, helping to establish the area as a center of iron and steel production.
In 1881 Aldrich founded the Cahaba Coal Company in Bibb County. After building a railroad connector, the company laid out a "model community" on the bank of Caffee Creek. After seeing a "ton block" of coal brought from the mine, Aldrich named the town Blocton. Blocton coal earned a reputation as an efficient fuel for steam locomotives and the profitable company embarked on a period of great expansion. Aldrich advertised widely for miners who arrived from all over the United States, as well as Western and Central Europe. By the summer of 1890 over 3,600 people were residents of Blocton and products from the companies' mines and overs were being sold to customers throughout the Southeast and parts of Latin America.
In addition to his many business interests, Aldrich pursued a lifelong fascination with shell collecting, eventually amassing one of the largest amateur collections of his time, partly by purchase and partly by collecting in person. In the 1890s he joined a "Shell Syndicate" to support naturalists Herbert H. Smith and Amelia W. (Daisy) Smith, who collected freshwater and terrestrial mollusks in Alabama and Georgia. State Geologist Eugene Allen Smith encouraged Aldrich to concentrate his efforts in the Tertiary paleontology of the Coastal Plain, often sending him material to identify, and Aldrich collected thousands of fossils from now-classic sites along the Alabama and Tombigbee Rivers, such as Claiborne. He contributed an article to Bulletin 1 of the Geological Survey of Alabama on the state's Eocene fossil record, including nine plates illustrating new species. His collection of modern shells is now in the Florida Museum of Natural History in Gainesville, and his fossil shells are in the Geological Survey of Alabama Paleontological Collection and the Alabama Museum of Natural History.
In 1896 Aldrich secured a nomination to the 54th United States Congress by contesting the election of Oscar W. Underwood. As a Republican in a largely Democratic state, Aldrich served for less than a year before being defeated by Underwood in the 1896 election. He returned to the coal business as president of the Cahaba Southern Mining Company, which operated mines at Hargrove in Bibb County. In 1899 be became a vice-president of the Birmingham Machinery and Foundry Company and, two years later, was named the acting president of the Sloss-Sheffield Steel & Iron Company. He also opened the Virginia mines, which were the site of a tragic explosion in 1905 that killed over 100 miners.
In 1902 Aldrich joined his son in a prospecting venture in Tallapoosa County called the Hillabee Gold Company. In 1905 he bought the Montevallo Mining Company back and served until 1910 as its president. In 1911 President William Howard Taft, who had been a neighbor in Cincinnati, Ohio, appointed him as Postmaster of Birmingham.
Aldrich's paleontological hobby became his career in later life, when Eugene Allen Smith appointed him as Curator of Paleontology of the Alabama Museum of Natural History. He donated large collections of Southeastern fossils, many from sites that are no long exposed today. Under Herbert and Daisy Smith, who were hired in 1909, the Museum continued his species-based cataloging system for fossils and Aldrich continued to write short articles on Tertiary mollusks. His research into the area's paleontology earned him wide esteem and he was awarded an honorary doctorate by the University of Alabama.
In 1930, the octogenarian Aldrich named new ichnogenera of fossil footprints that were discovered in a University of Alabama coalmine in Walker County, Alabama. Although his descriptions were brief, the well-reproduced photographic plates brought this work to attention when similar trackways were discovered in 1999 at the nearby Union Chapel Mine (now the Stephen C. Minkin Paleozoic Footprint Site).
E. A. Smith was a close friend of T. H. Aldrich, and named one of his sons Truman Aldrich Smith in his honor.
Truman Aldrich died in 1932 at the age of 83, and is buried at Birmingham's Elmwood Cemetery.