After serving as a pilot in World War II, Dunphy began his broadcast television career in 1953. He was the news director/anchor at then-CBS owned-and-operated (O&O) WXIX (now CW affiliated WVTV) in Milwaukee. Dunphy also was a sports reporter at another CBS O&O, WBBM-TV, in Chicago. Dunphy also served as a color commentator for Green Bay Packers telecasts on CBS in 1956.

In 1960, Dunphy took over the anchor chair at the Los Angeles CBS O&O station KNXT (now KCBS-TV), where he anchored Los Angeles' most popular newscast, later titled "The Big News", a program that often attracted a quarter of Los Angeles television owners, ratings unheard of in the market. He was still popular when fired in 1975, yet KNXT sought to adopt a faster-paced, "Eyewitness News" type format. It was then that Dunphy joined KABC-TV, bringing it to the top of the ratings, making it Southern California's news leader. Since Dunphy's unceremonious firing, Channel 2 never recovered in the ratings, until the mid-2000s. Dunphy left KABC-TV in 1989 and joined the upstart KCAL-TV that July (when it was still KHJ-TV) as one of the pioneering anchors of the three-hour primetime news format, "Prime 9 News". He returned to KCBS-TV in 1995 and remained until 1997 as an anchorman, and rejoined KCAL-TV in 1997, where he remained until his death.

Dunphy was one of the first newscasters to interview President Richard Nixon after his resignation in 1974. He would later sit down with Ronald Reagan, Jimmy Carter, and Gerald Ford. Dunphy also performed regular cameos in L.A.-based films including Warning Shot, Night of the Lepus, Oh God!, Short Cuts, The Jerky Boys and Independence Day, as well as in episode 6 of Batman Film Way,,,Way Out, and is considered to be the inspiration for two fictional television characters: Ted Baxter on The Mary Tyler Moore Show and Kent Brockman on The Simpsons (the director of "Krusty Gets Busted", Brad Bird, designed the character and modeled him after anchorman Ted Koppel.

Dunphy was also a songwriter. One of his songs was called, appropriately, "From the Desert to the Sea" and was recorded by country music star T.G. Sheppard.

On May 9, 1984, Dunphy received a star on the Hollywood Walk of Fame for his work in the television industry, located at 6669 Hollywood Boulevard. He succumbed to a heart attack on May 20, 2002.