The 44-year-old from Llangefni has been with the club for a number of years as a highly-rated coach, working with Jon Newby and then being Sinclair’s number two as assistant manager for the past 23 months.
“It has been a pleasure and honour to work alongside Frank and I thank him for that opportunity,” he said.
“With his unforeseen resignation the club have decided to continue with the same staff and I welcome the opportunity to drive the club forward and in achieving sustained membership of Conference North.
“I will get together with the management team to discuss the strategy and plans that we have in place and how we as a group of players and staff will implement that on the pitch and into games.
“The club, myself, management team and players all want the best for Colwyn Bay Football Club.”
“The foundation of the club is very strong and and we need to ensure that continues by working together with the community of Colwyn Bay to reflect strength in unity.”
Chairman David Titchiner said: “Gus knows the players and the club so well that it makes sense for him to take over now and cause the minimum of upheaval at a crucial stage of the season.”