Lamb, who has been involved with Boro since 1986, will retain a place on the club’s board as a non-executive director.
Lamb told Middlesbrough’s club website today: “After almost 25 years in the role during some of the most challenging, exciting and successful periods in the club’s history, the time is right for me to make way for someone else.
“I have enjoyed every minute of my time as chief executive and now look forward to exploring new opportunities and challenges.
“I want to thank all the staff who have given me their help and support during my time at the club. I am pleased that with Tony Mowbray and Mark Venus at the helm the club is able to look forward to an exciting future.”
And Boro chairman Steve Gibson said: “I want to thank Keith for his integrity, commitment, dedication and loyalty to the club and to me personally.
“Keith’s involvement has been crucial to the most successful period in the club’s history, including not only the move to the Riverside Stadium and the development of the Rockliffe training facility but also winning our first major trophy and reaching a European final.
“I am delighted that Keith will continue to work with the club as a non-executive director and this will enable us to draw on his wealth of experience and talent to fashion the future strategy of the club.”
