Sir Jonathan Michael, chief executive of Guy's and St Thomas' NHS Foundation Trust, has announced his resignation from SE1's hospitals to join BT.
Sir Jonathan will leave the SE1 hospitals in April and will join BT Health as deputy managing director (healthcare) this summer.
BT Health is responsible for the telecoms company's delivery of services to the health sector including three major NHS contracts.
"For the past six years I have had the tremendous privilege of being chief executive of two of London's most well known and successful teaching hospitals," Sir Jonathan said on Tuesday.
"Throughout my career, both as a consultant renal physician and during my 10 years experience as an NHS chief executive – most recently at Guy's and St Thomas' and previously at University Hospitals Birmingham – I have recognised the pivotal role that IT plays in the delivery of high quality health care."
Trust chair Patricia Moberly issued a statement paying tribute to Sir Jonathan's contribution and reassuring staff and patients that there would be a smooth handover to a successor: "All of us who have known the Trust during the past six and a half years are aware of the vast improvements which have taken place under his stewardship."
She continued: "Sir Jonathan has remained totally committed to the National Health Service, to the Trust and to his job, but having taken stock of his 37 years in the NHS, he has decided at this stage of his career to do something completely different and will be joining British Telecom in a senior position in their Healthcare Division."
Patricia Moberly added: "Personally, I shall miss Sir Jonathan's friendship, wisdom and above all his passion for the best possible clinical standards for our patients. I do however understand and respect his decision and wish him luck in his new venture. We have always worked very closely together and we will do our best to manage a smooth transition to his successor."
Sir Jonathan, 61, is married with 4 children. He was knighted in 2005.