In large part due to the anti-comic book campaign launched by Fredric Wertham's Seduction of the Innocent and the United States Senate Subcommittee on Juvenile Delinquency in 1953, most of Haney's publishers went out of business in the 1950s. In 1955 he connected with DC Comics and his first DC credit was the story "Frogman's Secret!" in All-American Men of War #17 (January 1955). Thus began a long association with DC, which lasted almost thirty years, with Haney scripting just about every sort of comic DC published.
Haney was the writer of the story "The Rock of Easy Co.!" in Our Army at War #81 (April 1959), the first appearance of Sgt. Rock. Haney and artist Lee Elias created the supervillain Eclipso in House of Secrets #61 (August 1963).
Haney frequently claimed to have co-created the Doom Patrol with Arnold Drake and worked with him on the first few issues, but Drake insisted that Haney worked on the first issue only, and that his only role in creating Doom Patrol was co-creating the character Negative Man.
In 1964, Haney created the Teen Titans with artists Bruno Premiani and Nick Cardy. Robin, Kid Flash, and Aqualad teamed up in The Brave and the Bold #54 (July 1964) to defeat a weather-controlling villain known as Mister Twister. They subsequently appeared under the name "Teen Titans" in The Brave and the Bold #60 in July 1965, joined by Wonder Woman's younger sister Wonder Girl in her first appearance. After next being featured in Showcase #59 (Dec. 1965), the team was spun off into their own series with Teen Titans #1 (February 1966).
The Metamorpho character was created by Haney and artist Ramona Fradon in The Brave and the Bold #57 (January 1965). Haney stated in 1995 that "The most creative single thing I ever did was Metamorpho". The character was featured in his own title, also written by Haney, from 1965 to 1968. Metamorpho later appeared in a series of back-up stories in Action Comics #413–418 and World's Finest Comics #218–220 and #229.
Haney and artist Howard Purcell created the supernatural character the Enchantress in Strange Adventures #187 (April 1966). The Enchantress appears in the 2016 live-action movie Suicide Squad, portrayed by actress Cara Delevingne.
Haney was the writer of many of the issues of including #59 (April–May 1965) which featured Batman's first team-up in the title. Haney scripted issue #85 (Aug.-Sept 1969) wherein artist Neal Adams updated Green Arrow's visual appearance by designing a new costume for the character. Haney frequently disregarded continuity by scripting stories which contradicted DC's canon or by writing major heroes in an out-of-character fashion. Haney himself, along with artist Jim Aparo, appeared as a character in The Brave and the Bold #124 (January 1976). Haney's final story of the series was a Batman and Kamandi team-up in issue #157 (Dec. 1979).