A revered grounds care professional, Millar's industry-wide reputation began at Wrest Park, Silsoe, Bedfordshire before joining Glasgow City Council.
Millar moved to Milton Keynes in 1989 and joined Milton Keynes Council as client officer in the Parks and Open Spaces Department.
Alex Millar became IoG chairman in 1991-1993 and held his current post as IoG National Chairman since 2002.
IoG chief executive Geoff Webb said: "Alex was someone who had a great perception and understanding of others; he was a person with immense knowledge and he was highly respected throughout the industry.
"I certainly will miss his company and his sense of intellect, guidance, humour and determination, as well as his vision that has been the catalyst for so much change at the IoG.
"If ever there was a true ‘unsung hero' and a champion for the industry, Alex had the perfect CV. I pay tribute to all that he has achieved over so many years of dedicated service to the IoG."
British and International Golf Greenkeepers' Association (BIGGA) chief executive John Pemberton added: "Alex's passion for the grounds care industry was immediately obvious.
"He was astute, likeable and a role model for others and anyone who spent time with him quickly appreciated being in his company. Alex was someone for whom I had the highest regard and he was the perfect gentleman who will be sadly missed by his friends and colleagues in greenkeeping and groundsmanship."
Amenity Forum chairman Jon Allbutt said it was a great loss to the industry.
"He had a great sense of humour and time for people, which is a rare thing," explained Allbutt.
"He was a very long-standing and dedicated member of his profession, an extremely nice bloke and always ready to help."
Alex Millar died on 17 February, aged 67.