Taggart, an Irish-born immigrant, came to the United States in 1861 at the age of five, grew up in Xenia, Ohio, and moved to Indiana as a teenager.

As state chairman in 1892, Taggart helped Cleveland carry Indiana in opposition to Harrison's bid for reelection.

In 1908 Taggart assisted in securing the Democratic nomination of John W. Kern for U.S. vice president and Thomas R. Marshall for governor of Indiana.

In addition to his political activities, Taggart was the owner and developer of the French Lick Springs Hotel in Orange County, Indiana; he also maintained a summer home at Hyannis Port, Massachusetts.

Young Taggart left high school early to work full-time at the depot's hotel and restaurant.

In 1875, when young Thomas was 18, his employer, the N. and G. Ohmer Company, sent him to Garrett, Indiana, to work in the restaurant at DeKalb House, a depot hotel.

Thomas remained at Garrett until 1877, when he was transferred to Indianapolis, Indiana, to work as a clerk for the Ohmer company's dining hall/restaurant at the city's Union Depot.

Known as a hard worker, Taggart became the depot restaurant's manager and eventually its sole owner in the new Union Station.

[2] In 1901 Taggart began his most ambitious and famous project when he organized a small group of investors that acquired and developed the French Lick Springs Hotel in Orange County, Indiana.

[16] Although casino gambling was illegal under Indiana law, it flourished in the Orange County area from the early 1900s until the mid-1940s, during the time the Taggart family managed the French Lick Springs Hotel, and contributed to the resort's popularity.

[3] Although the city's then-growing African American population generally supported Republicans until the New Deal, Indianapolis lawyers Alexander E. Manning (who became president of the National League of Negro Democrats in 1896) and James T.V.

[20][21] On March 20, 1916, Indiana governor Samuel M. Ralston appointed Taggart, his political ally, to the U.S. Senate to fill a seat left vacant by the death of Benjamin F. Shively.

[23][24] Taggart's health declined in the 1920s, but he remained active in national and state politics and civil affairs until his death in Indianapolis in 1929.

After a brief funeral service in the dining room of his North Delaware Street home in Indianapolis, he was buried at Crown Hill Cemetery.

[6][2] Following his death in 1929, Taggart's son, Thomas Douglas, became owner of the French Lick Springs Hotel property and buildings valued at nearly $2 million.

[12][25] Taggart is considered the "undisputed boss of the Democratic machine for the first quarter of the twentieth century"[26] and "one of Indiana’s most dominant political figures.