On January 16, 1949, KNBH, the station now known as NBC4 Southern California, began broadcasting on Channel 4 to the Los Angeles Designated Market Area (DMA). At that time, it was one of seven VHF stations licensed for operation in the market. KNBH, which stood for National Broadcasting Hollywood, was one of three stations in the market representing a national broadcasting chain. The station, which was owned by the National Broadcasting Company, debuted with three hours and forty minutes of programming, which followed a 15-minute test-pattern-and-music session. Inauguration night launched with an eighteen-minute newsreel, "Review of 1948," the market's first variety program "On With the Show," and the station's first live program "The Pickard Family," featuring Dad and Mom Pickard and their four children singing familiar American songs.

By October 1949, KNBH had extended its operating schedule from five to seven days a week, with approximately twenty-six hours of television programming each week. The station continued to make major technical advances and was the leading promoter of television as the premiere advertising medium. In October 1950, KNBH transmitted the first commercial telecast of a sports event, a Los Angeles Rams Football Game, via the Los Angeles/San Francisco inter-city MicroWave Relay. KNBH again made history in April 1951 when the first telecast, originating in the East, was presented to West Coast viewers on the same day. The station broadcast General Douglas MacArthur's speech before Congress less than five hours after it had been originated in Washington, D.C. In November 1962, the station relocated to the NBC Burbank facilities, its current location, and changed its call letters to KNBC.

When the station launched in 1949, Los Angeles was the fifth largest city in the United States, with only 80,000 television sets within 100 miles of the station's Mount Wilson transmitter. Today, the LA market is the second largest in the country and Channel 4 is viewed in more than five million households, reaching fifteen million viewers regularly. The station now operates 24 hours a day, seven days per week.

NBC4 was one of the first stations in the market to launch its own web site in August 1995. The site, located at www.nbc4.tv, receives more than 200,000 unique visitors per month. On October 24, 1998, NBC4 was the first station in the market to broadcast a High Definition signal.

In addition to carrying the network's award-winning daytime, prime-time and late night programming, NBC4 Southern California produces thirty-six hours of live, local news programming each week. A dominant station in the market, NBC4 Southern California is known for the quality of its daily newscasts, its community outreach and its coverage of major breaking news.