The second of two brothers, Daly was born in Johannesburg, South Africa, where his American father worked as a geologist. After his father died of tropical fever, Daly’s mother moved the family to Boston, Massachusetts, in the United States. Daly was an alumnus of Tilton School in Tilton, New Hampshire; he later served on its board of directors for many years and contributed to the construction or restoration of many buildings on campus. He did his post-secondary education at Boston College.  He married twice, first to Margaret Griswell Neal in January 1937. The marriage resulted in sons John Neal Daly and John Charles Daly III and daughter Helene Grant Daly. It ended in divorce in April 1959. On December 22, 1960, Daly married Virginia Warren, daughter of then–chief justice Earl Warren, in San Francisco. They were married for over 30 years, until Daly’s death. The marriage yielded three children: John Warren Daly, John Earl Jameson Daly, and Nina Elisabeth Daly.  Daly died in Chevy Chase, Maryland, of cardiac arrest.

Daly began his broadcasting career as a reporter for NBC Radio, and then for WJSV (now WTOP), the local CBS Radio Network affiliate in Washington, D.C., serving as CBS’ White House correspondent.  Through covering the Roosevelt White House, Daly became known to the national CBS audience as the network announcer for many of the President’s speeches. In late 1941, Daly transferred to New York City, where he became anchor of The World Today. During World War II, he covered the news from London as well as the North African and Italian fronts. Daly was a war correspondent in 1943 in Italy during Gen. George S. Patton’s infamous “slapping incidents”. After the war, he was a lead reporter on CBS Radio’s news/entertainment program CBS Is There (later known on TV as You Are There), which re-created the great events of history as if CBS correspondents were on the scene.  As a reporter for CBS, Daly was the voice of two historic announcements. He was the first national radio correspondent to deliver the news of the attack on Pearl Harbor on December 7, 1941, (recordings of this announcement reveal a minor error, either a mistyping of the copy in haste or a misreading by Daly as he pronounced Oahu as if it were spelled “O-ha-u”), and he was the first to relay the wire service report of the death of President Franklin Delano Roosevelt on April 12, 1945, interrupting “Wilderness Road” to deliver the news. Both narrations have been used on historical record albums and radio and TV retrospectives.

Daly’s first foray into television was as a panelist on the game show Celebrity Time. This led to a job in 1950 as the host and moderator on a new panel show produced by Goodson–Todman, What’s My Line? The show lasted 17 years with Daly hosting all but four episodes of the weekly series.  In 1954–55, in addition to his duties with What’s My Line?, Daly also hosted the final year of the NBC Television game show Who Said That?, in which celebrities tried to determine the speaker of quotations taken from recent news reports.  On What’s My Line?, each panelist introduced the next in line at the start of the show. Following the 1951 departure of panelist Louis Untermeyer, Random House co-founder and humorist Bennett Cerf joined the panel. Upon Fred Allen’s death in 1956, Cerf became the anchor panelist who would usually, but not always, introduce Daly. Cerf usually prefaced his introduction with a pun or joke that over time became a pun or joke at Daly’s expense. Daly would then often fire back his own retort. Cerf and Daly enjoyed a friendly feud from across the stage for the remainder of the history of the program. The mystery guest on the final CBS program (aired September 3, 1967) was Daly himself. (Over the years, many people had suggested this to Daly, but he could never do it, as he was always the “emergency mystery guest” in case the scheduled guest did not show up for the live program. Despite a few close calls, this plan was never needed.)

According to executive producer Gil Fates, Daly was resistant to changes that would have appealed to a younger audience but might have diminished the show’s dignity. For example, Daly usually referred to the panelists formally, e.g., as “Mr. Cerf.” The producers, Fates said, were unable to challenge Daly for fear of losing him as the show’s moderator. The series spawned a brief radio version in 1952 that was also hosted by Daly. The series also inspired a multitude of concurrent international versions and a syndicated U.S. revival in 1968 in which Daly did not participate.  Daly also did hosting duties on Who Said That?, It’s News to Me, We Take Your Word, and Open Hearing and was a narrator on The Voice of Firestone starting in 1958.  He also had several television and movie guest appearances from the late 1940’s to the mid-1960’s, including an uncredited role in Bye Bye Birdie (as the reporter announcing the title character’s induction into the Army) and as the narrator, in a mock documentary style, on the premiere episode of Green Acres.  In 1949 he starred in the short-lived CBS Television newspaper drama The Front Page, where it was thought that his presence and journalistic experience would give the series more authenticity.

During the 1950’s, Daly became the vice president in charge of news, special events, and public affairs, religious programs and sports for ABC and won three Peabody Awards. From 1953 to 1960, he anchored ABC news broadcasts and was the face of the network’s news division, even though What’s My Line? was then on CBS. At the time, this was a very rare instance of a television personality working on two different networks simultaneously. (Technically, Daly worked for Goodson–Todman Productions for What’s My Line?, and also filled in occasionally on The Today Show on NBC, making him one of the few people in early television to work simultaneously on all three networks.) His closing line on the ABC newscast was “Good night, and a good tomorrow.” Daly resigned from ABC on November 16, 1960 after the network preempted the first hour of election night coverage to show Bugs Bunny cartoons and The Rifleman from 7:30 to 8:30 while CBS and NBC were covering returns from the Kennedy–Nixon presidential election and other major races.

Daly continued on What’s My Line? until 1967. In the 1962–63 season, the program was in competition with Howard K. Smith’s News and Comment program on ABC. A former CBS correspondent, Smith switched networks early in 1961, by which time Daly had already resigned from ABC. Smith later took over Daly’s former role as anchor of ABC’s evening news broadcast.  In May 1967, during the final year of What’s My Line?, it was announced that Daly would become the director of the Voice of America after the show ended. He assumed the position on September 20, 1967, but lasted only until June 6, 1968, when he resigned over a claim that Leonard H. Marks, his superior at the U.S. Information Agency, had been making personnel changes behind Daly’s back.  Daly retreated from the public eye. He did not host the syndicated version of What’s My Line?, although he did co-host a 25th-anniversary program about the show for ABC in 1975. He was a frequent forum moderator for the conservative think tank the American Enterprise Institute throughout the 1980s.