On May 1, 1922, it had sponsored the debut program on WAAK, Milwaukee's first radio station, which was owned by the local division of the Gimbel's department store chain.

[15] WTMJ aired a full service format featuring a mixture of music, news, talk and local personalities along with sports play-by-play, as well as dramas, comedies and other programs from NBC.

[17] On November 11, 1928, as part of a major nationwide allocation under the provisions of the Federal Radio Commission's General Order 40, WTMJ was reassigned to its current frequency of 620 kHz.

WFLA-WSUN turned to the engineering community to determine whether a then-theoretical concept of a directional antenna could be installed to reduce the Florida station's signal toward Milwaukee.

[20] (WFLA moved to 970 kHz in 1941, with WSUN taking its place in Tampa, followed by the current-day WDAE) In 1942, a new facility, The Milwaukee Journal's Radio City, opened for WTMJ and its FM sister station, W55M (later WMFM and WTMJ-FM), in addition to the yet-to-come WTMJ-TV.

[28] In 1993, WTMJ hired two new talk show hosts, liberal Jay Marvin and conservative Charlie Sykes.

[33] In 2002, Sykes and fellow WTMJ host Jeff Wagner led a campaign to recall Milwaukee County Executive Tom Ament, who was embroiled in scandal for abusing the county pension system; Ament controversially retired at the end of February 2002, rather than resign.

In March, Journal Communications fired program director Joe Scialfa, who had been with the station for 14 years beginning as producer for the Charlie Sykes show.

[41] The transmitter, formerly individually licensed to Frank Glass McCoy and leased to Scripps (who owns the physical tower and transmitter assets) and operated by Good Karma Brands, was formerly licensed to Waukegan, Illinois, and translated Kenosha public radio station WGTD before the move of the translator to Milwaukee.

Additionally, the station is simulcast at 88.5 FM within the campus of American Family Field, allowing fans attending Brewers games to listen to the radio play-by-play of the game without the broadcast delay presented both by the satellite delay to WTMJ's studios, and for regulatory reasons.

[44] On July 27, 2018, as part of its exit from radio, Scripps announced the sale of WTMJ and WKTI to Good Karma Brands.

[45] Morgan Murphy Media and other local groups have made investments in Good Karma Brands to back the purchase.

[46] Good Karma took control of WTMJ and WKTI on November 1, 2018, thus separating the AM station from its TV cousin for the first time.

[47] Shortly after, WTMJ's HD Radio transmitter was taken out of service as the station had since established an FM translator.

[49] WTMJ's final Packers broadcast was the NFC Divisional game, a 13–10 loss to the San Francisco 49ers on January 22, 2022.

[50] On September 28, 2022, WTMJ, WKTI and WGKB departed Radio City for new showcase studios based in The Avenue MKE, within the Third Street Market Hall, two blocks from where it first broadcast as WCAY only a few months after the license's centennial.

During the midday, the station airs live, local talk shows with Jeff Wagner and Steve Scaffidi.

[52][53] During weekends the station airs a mixture of local how-to programming, talk shows, local sports talk programs, sports play-by-play and national talk shows, for instance The Truth About Your Future with Ric Edelman and Compass Media Networks' This Weekend with Gordon Deal, in addition to ABC News' Perspective news magazine, the CBS News Weekend Roundup, and CBS's podcast The Takeout with Major Garrett.

For eighty years, WTMJ was based at 720 East Capitol Drive in Milwaukee, in an Art Deco facility known as "Radio City" in tribute to the New York complex of the same name.

[17] Four towers are used during the day, providing city-grade coverage to most of eastern Wisconsin (including Madison and Green Bay) and northern Illinois, with most of the Chicago area getting at least a grade B signal.

At night, power is fed to all six towers in a directional pattern, concentrating the signal in Milwaukee, Green Bay, and Chicago.