The President of United Earth is the head of state for United Earth. (SCE eBook: The Future Begins, ST novel: Starfleet: Year One)

In the early 2160s, Lydia Littlejohn was the President of United Earth, and was in office when the Articles of the Federation were signed, establishing the United Federation of Planets. (SCE eBook: The Future Begins, ST novel: Starfleet: Year One)

In 2160, President Littlejohn personally monitored post-war negotiations with the Romulan Star Empire and kept an official office in San Francisco. (ST novel: Starfleet: Year One)

The Tales of the Dominion War short story "Eleven Hours Out" also established a role of Prime Minister of United Earth, which is confirmed by the ENT novels The Good That Men Do and Beneath the Raptor's Wing. The exact nature and extent of the President’s role, and how it functions alongside the role of Prime Minister, are as yet unestablished.