In positions as senior and executive vice president, Littlefield was second among program executives to Tartikoff alone and became known as his heir apparent. Despite a rocky working relationship which included a lot of what Littlefield has termed "respectful fighting" in which his judgment was sometimes questioned by his superior, Tartikoff and Littlefield enjoyed a singularly productive tenure at NBC together. After Tartikoff gradually severed his tie with the slipping NBC in the early 90s to became chair of Paramount, the even-keeled Littlefield stepped into his high-pressure shoes, declaring his interest in promoting fictional drama series as NBC's mainstay rather than relying on an excess of sitcoms, reality-based programming or TV movies. Under Littlefield, the network enjoyed a long run as the Number One network but as decade drew to a close, NBC's ratings share began to dip. Just shy of his 20th anniversary with the network, Littlefield stepped down and entered into a non-exclusive program development deal with his former employer.
In 1999, he formed Littlefield Co., a TV production firm that focused on broadcast properties that also could be exploited on the Internet.