WCJB-TV began operation on April 7, 1971, as an NBC affiliate. The first owner of the station was William E. Minshall. The first programming originated in Jacksonville, and it was sent by microwave from a station there to a relay site at Camp Blanding and from there to Gainesville for broadcast.

In 1973, WCJB-TV became an ABC affiliate which it has remained to this day.  In 2009 WCJB also became a CW affiliate.

Diversified Communications, headquartered in Portland, Maine, purchased WCJB-TV on October 12, 1976 and continues to own the station. Diversifed also owns a television station in Bangor Maine.

The station first started broadcasting from a small building on NW 43rd Street, north of the city of Gainesville. At the time, NW 43rd was a dirt road and the station was "out in the country". The road, now a major artery, was not paved until 1979. 

The station's first studio cameras did not have camera operators - they were remotely controlled. Commercials consisted of 16mm film and 35mm color slides. Any 16mm film shot for the newscasts had to be at the station by 2:00 PM so it could be taken to Jernigans to be processed. It was picked up at 3:45 PM, brought back to the station and edited for air. 

WCJB-TV20's building was extensively remodeled and expanded in the mid-1980's, adding a new news department, production office, management offices and other facilities. The station now employs approximately 85 people, compared to fewer than 20 when the station first signed on in 1971. The station also maintains a studio in Ocala for live news broadcasts from Marion County.

In July 2008, WCJB-TV completed an extensive renovation project.  It included a new home for an expanded newsroom, plus new offices for production and sales areas.  The rest of the building also received a fresh and updated look.

WCJB made the switch to digital-only broadcasting in February 2009.  It included adding the latest in automation and transmission equipment.  The transition also led up to the debut of a new logo and news set in May 2009.