In the early years, the company's business consisted primarily of low-premium, low-benefit "sick and accident" policies, a form of disability insurance which paid the owner a stated weekly amount for every week he was unable to work due to illness or injury. In order to prevent fraud, it was necessary for the amount of the benefit to be somewhat less than what the insured earned through regular employment. The vast majority of these policies, especially in the early years, were sold on the "debit system" (also called "home service insurance"), meaning that an insurance agent employed by the company, usually the one responsible for selling the policy initially, made periodic visits to the clients home to collect the premium (and, generally, to sell or attempt to sell more insurance). The frequency of these visits varied, but was usually, especially in the early years, weekly; in later years, more of the collection visits were on a biweekly or monthly basis.
The company soon expanded into "industrial life insurance", so-called because it was generally aimed at industrial workers, which was also sold on the debit system, and accidental death and dismemberment insurance, which rather than a weekly income paid a stated, fixed amount, if the insured were to die by accident or lose the sight or use of an eye or a limb. The industrial life insurance plans were usually for small face amounts: typically $250, $500, or $1000 in the early years, and featured double indemnity for accidental loss of life, which could be triple indemnity or even more if death were to occur as the result of an accident on a public conveyance. (For this reason these plans were often derided by their detractors as "streetcar insurance.")
The company gradually expanded its operations to the southern eastern seaboard and eventually covered most of the continental U.S. excepting the northeastern states, the Rocky Mountain states, and the Pacific Northwest. It also began to write "ordinary life" insurance to better risks, such as middle class office workers, religious ministers, accountants, bankers, and similar persons. Its greatest marketing development, however, was probably its beginning WSM radio in 1923. Taking its callsign from the company's motto, We Shield Millions (which was in turn taken from its shield-shaped logo), the station began to broadcast advertising, including the company's own messages, over its powerful 50,000-watt clear channel signal, its studios initially located within the National Life office building in downtown Nashville. In 1925, management began the program that was soon the become the Grand Ole Opry, which made country music (then generally referred to as "hillbilly music") more mainstream than it had been previously. In 1950, the company spawned Nashville's first television station, WSM-TV (now WSMV-TV).
The company, along with nearly all U.S. life insurers, faced a crisis with the coming of the Great Depression in 1929; like many of them, it survived largely by offering its clients policy loans against the plans' cash values. With World War II came another crisis due to the manpower shortage brought about by conscription; in some areas, premium collections, at least on a weekly basis, had to be curtailed (gasoline rationing played a factor here as well) and many clients who were used to having their premiums collected in person by an agent found themselves having to take the initiative to mail in their premiums or lose their coverage.
By the mid-1960s the company had outgrown its home office location in downtown Nashville. It had also been somewhat shamed when one of its principal competitors, the Life and Casualty Insurance Company of Tennessee ("L&C"), had built a 31-story skyscraper which had opened in 1957 and which had been, briefly, Nashville's only skyscraper and the tallest building in the Southeast. The new National Life building, across the street from the Tennessee State Capitol, had only 30 stories but was both considerably larger and located on higher ground, so it appeared to be grander than that of its rival, which was part of the intended effect. By this point, the television studios of WSM (which had begun in 1950 and was the first Nashville television station) had already been moved to a location in West Nashville near the stations transmitting tower; the radio stations were soon to follow. About the same time as plans were finalized to move the station, a plan was announced to build a theme park on the property of Rudy's Farm, a sausage company located in the Pennington Bend of the Cumberland River. This park opened in 1972 and was known as "Opryland USA". Other than the usual selection of thrill rides and "kiddie rides", the park featured shows of all genres of American music, not just country. Construction began on the new Grand Ole Opry House at about the same time, and the Opry left the Ryman Auditorium for the new facility in the summer of 1974. At about the same time as the home office move was undertaken, a holding company was formed to buy all National Life stock. This organization was known as "NLT Corporation", with the "NL" standing for "National Life" and the "T" standing for Third National Bank, one of Nashville's leading banks at the time (acquired in the 1990s by SunTrust). However, then-existing banking laws and regulations thwarted the attempt to acquire Third National; however, the holding company business form was maintained.
Another important development of the 1970s was the phasing out of weekly premiums; the former weekly premium amount was multiplied by 4.3 and became the monthly premium for the coverage.
In the early 1980s, Houston's American General Corporation, another insurance holding company, announced a hostile takeover bid for NLT. NLT made a counter-offer to buy out AGC, but in the end AGC, which had owned rival Life and Casualty since the 1960s, triumphed. AGC began to make plans to merge the former rivals (not fully completed until almost the end of the decade), and also to spin-off the "non-core" assets of NLT, particularly the entertainment properties. The Grand Ole Opry, the Opryland theme park, and WSM were sold to what became Gaylord Entertainment Company. American General would later merge into New York-based American International Group (AIG). Its division of the corporation is now branded as American General.
In the late 1990s the former National Life/American General building was sold to the State of Tennessee and is today known as the William R. Snodgrass Tower, named in honor of the state's former comptroller.