He announced the decision in a letter to staff, saying he had always intended to finish in 2014 since he was appointed in September 2004.
“By that date, I shall have completed ten years as principal, which I believe is long enough for any individual to hold such a rewarding and demanding position,” he said.
“The new principal will have the opportunity to take the college forward into what, in many respects, will be a new era for King’s and for UK higher education.
“In the 2014-15 academic year the results of the research excellence framework will be published, the decisions of the forthcoming spending review will start to be implemented and the next general election will take place.”
Professor Trainor, who was president of Universities UK between 2007 and 2009, said he will not retire, but did not indicate what future role he might hold.
The US-born academic, a former Rhodes Scholar at the University of Oxford, is one of the few university leaders to transfer from a post-92 university to a pre-92 institution having previously been vice-chancellor of the University of Greenwich.
The Marquess of Douro, chairman of King’s governing council, paid tribute to Professor Trainor.
“Professor Trainor has been a highly distinguished leader of the college,” he said.
“Under his guidance the college’s academic strengths have improved substantially over the past eight-and-a-half years”.
He mentioned how King’s had become one of only five Academic Health Sciences Centres in the UK and one of the three university members of the Francis Crick Institute, while also pointing to the £400 million that had been raised towards its £500 million fundraising campaign.
“On behalf of the whole college community, I wish to extend our gratitude to Professor Trainor for his skill and commitment in progressing the college’s interests since 2004,” said Lord Douro.
Beginning at its meeting on 12 March, the college council will now initiate a global search for Professor Trainor’s successor, a King’s spokesman said.