Christopher reigned as pope from 903 to 904. Some say he was an antipope, but although he did not become pope in the usual way, he was officially recognized as pope some time later. He is included in most modern lists of popes.

Christopher became pope by forcibly dethroning his predecessor, Pope Leo V, and putting him into prison, seemingly about October 903. As Leo appears to have soon died in his prison, Christopher has been regarded as his successor. This was during a corrupt time in papal Rome, and it is hard to tell what was true or not about Christopher. It is believed he was the first pope who stated that the Holy Ghost proceeded "from the Father and from the Son". Other than this and little else, nothing is known for certain about Pope Christopher.

He was driven from the papacy by his successor, Pope Sergius III in January 904. He then ended his days as a religious man, and some people say he was later strangled in prison. However, even this is mysterious.