Mr Morrison, 70, of West Fenton, led a distinguished life in a variety of roles - most prominently as the Queen's representative in East Lothian and, for a number of years, as Chief Scout of the United Kingdom.
Knighted in 2007, one of his proudest moments came when he attended the wedding of the Duke and Duchess of Cambridge in April 2011.
Sir Garth had been diagnosed in November with cancer of the oesophagus, for which he received successful treatment and an operation.
However, the disease returned, with the news coming just six days before he passed away that he had only weeks to live.
Lady Gill Morrison, his wife, told the Courier: "He had a very strong faith and we both discussed the fact that we come into this world and we go out of it, and we've had 43 very happy years together.
"He was very loved and I think it's because he had such an even temperament.
"You talk about people having an edge, but he had no edge at all. He was just a very warm person. He quietly got on with what he was doing but appreciative of what other people were doing.
"We were very lucky - he was a great guy."
Sir Garth became Lord Lieutenant in 2001, succeeding Sir Hew Hamilton-Dalrymple upon his retirement.
He was involved in several royal visits to the county and carried out duties such as delivering telegrams from the Queen to those celebrating 100th birthdays.
Sir Garth was also a High Constable of Holyrood House.
His personal interests included being chair of the Lamp of Lothian Trust, and running his farm at West Fenton - most recently a grain producer.
He and Gill also set up the Murfield Riding Therapy facility near their home, which Gill is still involved with today.
The couple had three children - Alastair, Clare and Christopher - and six grandchildren.
She added: "He went from one uniform to another - from the Navy to the Scouts, to High Constable to his Lord Lieutenant's uniform.
"He enjoyed the hundredth birthday cards because they got more and more lively. He was dancing with [North Berwick 100-year-old] Agnes Willens a few weeks ago!
"And he very much enjoyed that last duty he had, when the soldiers were made Freemen of East Lothian [at a homecoming parade in Haddington in April]."
A spokeswoman for Buckingham Palace said that the Queen had sent her personal condolences to Sir Garth's family.
Michael Williams, Vice Lord Lieutenant of East Lothian - who has been appointed Sir Garth's temporary replacement - said: "He was held in huge regard by a very wide community of people, and he was such a great leader.
"He was unbelievably hard working at what he did and he did his homework very well. He is going to be sorely missed."
Patrick Gammell, a Deputy Lord Lieutenant of East Lothian and Sir Garth's vice-chair on the Lamp of Lothian Trust, added: "He always had a great interest in youth, and everyone from all backgrounds getting on in life. He will be a very hard act to follow."
Councillor Ludovic Broun-Lindsay, Provost of East Lothian, said: "His passing is a great loss to the county.
"One of Sir Garth's last duties as Lord Lieutenant was to attend the parade marking the presentation of the Freedom of East Lothian to the Royal Regiment of Scotland.
"I was delighted that he was able to be there and felt the great pride and joy he had as he took the salute that day."
Councillor Willie Innes, leader of East Lothian Council, said: "Garth Morrison was a very thoughtful and conscientious man who carried out his role as Lord Lieutenant with great dedication. He had strong East Lothian roots and made a big contribution to the life of the county."
A private family funeral was to be held this week, followed by a thanksgiving service at St Mary's Parish Church, Haddington, at 2pm on June 21.