Dr. John Carter is a fictional medical doctor from the television series ER. He is portrayed by Noah Wyle. Dr. Carter is unique in that he was the only remaining major character to have stayed with the show from the beginning of the series up to the 2004-2005 season.

John Carter was from a wealthy family; consequently, he did not have any student loans from studying medicine.

Dr. Carter initially came to County General as a third year medical student. He initially was interested in surgery, but eventually changed his specialty to emergency medicine while studying under Doctor Peter Benton.

Dr. Carter was stabbed by a mentally ill patient. His friend and medical student Lucy Knight was also stabbed by the same man, but she did not survive her injuries. Dr. Carter eventually developed an addiction to drugs, and was taken to an inpatient treatment center in Atlanta by Dr. Benton.

Dr. Carter and Abby Lockhart had an on-again, off-again romance throught much of their time on the show together. Not long before the final breakup, Carter was going to ask Lockhart to marry him, but she made it clear that marriage was not in their future. The end came while Carter was in Africa. After his return, they have remained friends.

When Dr. Kovac was reported killed in Africa, Carter went to retrieve his body. To his surprise, he found that Kovac was still alive, and that another man had been mistaken for him. After arranging for Kovac to be sent home, Dr. Carter remained in Africa for several months. He worked to help locals who had been stricken with AIDS. He also fell in love with Kem. Kem soon became pregnant with Carter's child. Dr. Carter and Kem soon returned to the United States, and Carter returned to work at County General. However, Kem lost the baby - a boy - in the final months of her pregnancy.

In September of 2004, Noah Wyle announced that he would not renew his contract after it expired at the end of the 2004-2005 season. However, he has stated that he does not want Carter's story to end and may make occasional guest appearances after he leaves. The particulars of how Carter will be written out of the series have not yet been revealed.