McMaster will oversee the agency's 30-strong digital team and will report to chief executive Tim Bonnet. It is not known whether Sycamore has a job to go to.
Bonnet said: "Simon has done an outstanding job over the last seven years, building our digital offering and making it an essential part of our integrated approach. I am confident he will continue to develop our potential and deliver world class interactive work for our clients."
McMaster joined Tequila in 1999 and was instrumental in developing the agency's digital business.
McMaster said: "It's a tremendous opportunity to lead such a strong creative and technical team. I'm looking forward to pushing the boundaries of what digital can do for our clients."
Tequila's digital clients include Abbey, The Army, Canon, News International and Prudential.
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