This tall, bald and usually bespectacled character actor often portrayed pompous, prissy, and/or imperious figures. He made appearances on The Jack Benny Program as a salesman and a barber, and on NBC's Happy as a hotel manager. He had a brief role in Alfred Hitchcock's film The Birds (1963) as Mitch's (Rod Taylor) neighbor who advises Melanie (Tippi Hedren) that Mitch has gone to Bodega Bay for the weekend. He played a larger role in the original Invasion of the Body Snatchers (1956), as a physician in the "book-end" sequences added to the beginning and end of this film after its original previews.
In Billy Wilder's 1957 film adaptation of Charles Lindbergh's The Spirit of St. Louis, Deacon portrayed the chairman of the Columbia Aircraft Corp, Charles A. Levine, who, in February 1927, refused to sell Lindbergh his company's recently acquired Bellanca monoplane for Lindbergh's trans-atlantic flight unless his company could choose the pilot.
His best-known roles are Mel Cooley on CBS's The Dick Van Dyke Show (1961–1966) and Fred Rutherford on Leave It to Beaver (1957–1963), although Deacon played Mr. Baxter in the 1957 Beaver pilot episode "It's a Small World". He co-starred as Tallulah Bankhead's butler in a classic episode of The Lucy-Desi Comedy Hour called "The Celebrity Next Door". Deacon played Roger Buell on the second season of TV's The Mothers-in-Law (1967–1969), having replaced Roger C. Carmel in the role. He played "Principal 'Jazz-Bow' Conroy" in The Danny Thomas Show (1958).
In Carousel (1956), the film adaptation of the classic Rodgers & Hammerstein stage musical, Deacon had a bit role as the policeman who admonishes Shirley Jones (Julie) and John Dehner (Mr. Bascombe) about Gordon MacRae (Billy Bigelow) in the famous "bench scene". It was one of the few films in which he did not wear glasses, as were his roles in Abbott and Costello Meet the Mummy (1955), and the 1954 costumer Désirée, where he played Jean Simmons' elder brother, an 18th-century Marseilles silk merchant. Philadelphia-native Deacon played the role of Morton Stearnes' butler, George Archibald, in The Young Philadelphians (1959), starring Paul Newman. He played an imbibing Justice of the Peace, Reverend Zaron, in the classic 1957 Budd Boetticher directed western Decision at Sundown.
Deacon appeared in many sitcoms, including It's a Great Life, The People's Choice, How to Marry a Millionaire, Guestward, Ho!, Pete and Gladys, The Donna Reed Show, The Real McCoys (in the episode "The Tax Man Cometh", he clashes with series star Walter Brennan as Grandpa Amos McCoy over property tax assessments in the San Fernando Valley), Get Smart, Bonanza (a deceitful character who cheats the Cartwrights during their visit to San Francisco), and The Rifleman (episode "The Hangman", in an uncredited role). In episode 5 of the first 1964 season of the The Munsters, "Pike's Pique", he plays a Water District Commissioner, Mr. Pike, buying the underground right to lay pipe. In the The Addams Family, he administers Cousin Itt a battery of psychological tests in the May 1965 episode "Cousin Itt and the Vocational Counselor". In 1966, he appeared on Phyllis Diller's short-lived television sitcom, The Pruitts of Southampton. He also guest starred in the NBC family drama National Velvet, and in the ABC/Warner Brothers crime drama Bourbon Street Beat, and on the The Twilight Zone in the 1964 episode "The Brain Center at Whipple's". In 1967, Deacon played Ralph Yarby, director of security for lumber baron D.J. Mulrooney, in Disney's The Gnome-Mobile. In 1968, he played Dean Wheaton in the Walt Disney film Blackbeard's Ghost.
In 1983, Deacon reprised his role of Fred Rutherford in the television movie Still the Beaver, a sequel to the TV series Leave it to Beaver, which aired from 1957 to 1963.