Born in Canton, Ohio, Paar began his broadcasting career in radio, working first in Cleveland, Ohio and later, throughout the Midwest. During World War II, he was part of a special services company that entertained troops in the South Pacific. After the war, Paar tried his hand at acting and comedy, frequently appearing on . It was during an impressive stint as a guest host on Jack Benny's radio show that he caught the attention of NBC officials who eventually offered him his best known role, host of

In 1959, he was criticized for his interview with Cuban dictator Fidel Castro. Two years later, he broadcast his show from Berlin just as the Berlin Wall was going up.

Paar was often emotional and unpredictable. The most salient example of this kind of on-screen behavior was demonstrated in 1960. One of his jokes was cut from a broadcast by studio censors. The joke in question involved a woman writing to a vacation resort and inquiring about the availability of a "W.C." The woman used that term to mean "water closet" (i.e. bathroom), but the gentleman who received the letter misunderstood "W.C." to mean "wayside chapel" (i.e. church). The full text of the joke reveals multiple double entendres that are tame by today's standards, but too much for the network to bear in 1960. NBC replaced that section of the show with news coverage.

The decision to censor the joke so angered Paar that the next night, February 11, he announced on the air that he was leaving the show, saying "I've made a decision about what I'm going to do. I'm leaving . There must be a better way to make a living than this, a way of entertaining people without being constantly involved in some form of controversy. I love NBC [...] But they let me down." After finishing this monologue, Paar abruptly walked offstage, leaving his flustered announcer, Hugh Downs, to finish the show for him.

Less than a month later Paar was convinced to return; on March 7 he opened his monologue with the now-famous line, "As I was saying before I was interrupted..." He then went on to explain his departure with typical frankness: "Leaving the show was a childish and perhaps emotional thing. I have been guilty of such action in the past and will perhaps be again. I'm totally unable to hide what I feel. It is not an asset in show business, but I shall do the best I can to amuse and entertain you and let other people speak freely, as I have in the past."

Paar's emotionality made the everyday routine of putting together a ninety-minute entertainment program too difficult to continue for long. Indeed, Paar made it clear in his last season of in March, 1962 featured him sitting alone on a stool onstage, sharing a discussion he had had with his daughter, who insisted on calling his departure a sabbatical. Noting the origins of the term, he said that his own field was, though not completely used up, "a little dry recently." Then he called to his German shepherd who came to him from the seats of what was, for once, an empty studio, and walked out.

Later that same year, Paar began hosting a prime-time Friday night show on NBC. It is generally believed that The Beatles were introduced to American television viewers on , but in fact, they debuted on Paar's prime time hour. The show was significant because of its world view. Besides the Beatles, it debuted acts from around the world and also showed films from exotic locations. Paar's prime time show lasted for three years.

Paar came back for another late-night show in January 1975, on ABC—this time, as one of a group of rotating hosts on

Paar died at his Greenwich, Connecticut home in January 2004, at age 85, with his wife and daughter by his side. He had long been ill, having undergone triple-bypass heart surgery in 1998 and a stroke one year before he died.