Christopher began working on the NBC medical drama ER as a director and producer with the first season. He was promoted to co-executive producer midway through the third season. Christopher became an executive producer during the fifth season, but relinquished the position in the sixth season in order to focus on the development of Third Watch. He remained a consulting producer on ER until he returned to the position of executive producer at the start of the tenth season. Christopher was an executive producer from the tenth season until the series ended with the fifteenth season. He continued to regularly direct episodes throughout the series run and has helmed a total of 41 episodes as of the close of the fourteenth season.
Christopher and the rest of the producers of ER were nominated for an Emmy award for Outstanding Drama Series for their work on the first season at the 1995 awards. The series won the award the following year and Christopher was personally nominated for the Emmy award for Outstanding Individual Achievement in Directing for a Drama Series for his work on the episode "Hell and High Water". Christopher won the DGA Award for Outstanding Directorial Achievement in Dramatic Series for his work on Hell and High Water in 1996. Christopher won the award again in 1997 for his work on the episode Fear of Flying and also received a DGA diversity award along with John Wells for their promotion of a diverse workforce in the television industry.
Christopher was nominated for two prizes at the 1997 Emmy awards. Christopher was personally nominated for the Directing Emmy again in 2004 for his work on the episode The Lost.
Christopher was also nominated for two further DGA Awards for his directing work on ER. He was nominated in 1998 for the episode Fathers and Sons and in 2005 for the episode Time of Death.
In 1999 Christopher's fellow ER producer John Wells created Third Watch and enlisted Christopher to direct the pilot episode. Christopher came on board as an executive producer on the series from the pilot until its cancellation at the close of its sixth season in 2005. Christopher directed several episodes of Third Watch and was executive producer to consulting producer. Jonathan Kaplan became ER's producer and director in Christoper's place.
Other Wells Prodcution Series
In 2001 Christopher directed the pilot episode and executive produced Wells Production's next two series Citizen Baines and Presidio Med. Both series were short-lived and were cancelled before completing their first seasons.
In 2005 Wells created a new series named Smith and again recruited Christopher to direct the pilot episode. Christopher directed four episodes of Smith and was again credited as an executive producer but the series was cancelled shortly after it began airing. The series star Ray Liotta was also directed by Christopher as a special guest star in the Time of Death ER episode that earned Christopher DGA award nomination.
In the 2008 to 2009 television season Christopher developed the police drama series Southland for NBC. He worked with writing partner John Wells and creator Ann Biderman. Christopher, Wells and Biderman were executive producer for the first season and Christopher directed the pilot episode Unknown Trouble. The series was picked up and aired as a midseason replacement. Christopher directed the episodes See the Woman, Sally in the Alley and the season finale Derailed.
The series was renewed for a second season and Christopher remained an executive producer and regular director. He helmed the season premiere Phase Three and the episode U-Boat. NBC canceled the series before any episodes from the second season had aired. The six produced episodes were picked up by TNT and aired as the second season. TNT renewed the series for a third season and Christopher returned in the same role. He directed the season premiere Let It Snow, the episodes Punching Water, The Winds, Fixing A Hole and the season finale Graduation Day.