At TNT, Ernie Johnson known as "E.J.", works as the studio host for the network's coverage of the NBA, working pregame and halftime shows, as well as hosting the network's famous studio show that airs after each NBA doubleheader, Inside the NBA. At the end of each broadcast, Ernie presents "E.J.'s Neat-o-Stat of the Night," which has become a popular part of the show. For all NBA-related shows, Johnson is joined by former NBA stars Kenny Smith and Charles Barkley, and, on occasion, Magic Johnson and/or Reggie Miller. In addition to working basketball, Johnson is also the play-by-play announcer for TNT's PGA TOUR coverage. At TBS, Johnson works as the studio host for their coverage of college football. In 2002, Johnson was co-winner of the Sports Emmy for Outstanding Sports Personality, Studio Host, tying with Bob Costas of NBC and HBO. It was the first time Johnson had been nominated for a Sports Emmy.

Johnson's past work at TNT included roles as studio host for The Championships, Wimbledon from 2000 to 2002, in addition to working several roles at the 1994, 1998, and 2001 Goodwill Games, as well as the 1992 Winter Olympics in Albertville, France and the 1994 Winter Olympics in Lillehammer. He also co-hosted Barkley's now-defunct talk show, Listen Up! Past work at TBS also included working as studio host for their NBA coverage. Johnson also called weightlifting for NBC's coverage of the 2000 Summer Olympics in Sydney.

Johnson's career began in 1977 while he was still a student at the University of Georgia, taking a job as the news and sports director for the radio station WAGQ-FM in Athens, Georgia. He held that job until 1978. In 1979, Johnson began his broadcasting career in Macon, Georgia, joining WMAZ-TV after graduating. He worked there as a news anchor until 1981, when he moved to Spartanburg, South Carolina to work as a news reporter at WSPA-TV. Johnson moved back to Georgia in 1982, this time taking a job in Atlanta at WSB-TV as a general assignment news reporter. He became the station's weekend sports anchor and reporter in 1983. He held those jobs until 1989, when he left to join Turner Sports. From 1993 to 1996, Johnson called Atlanta Braves baseball games for SportSouth (now FSN South), where he had a unique broadcaster partner his father, Ernie Johnson Sr., a former Major League Baseball pitcher and Braves play-by-play announcer.