Close to a thousand mourners packed into and outside the Mary Immaculate Church in Waverley in Sydney's eastern suburbs on Wednesday for the two hour service, reports RugbyHeaven website.
Brumbies and former NSW Waratahs forward Mackay died last week aged 26 after being hit by a car in Durban late last month.
Mourners included Australian Rugby Union chief John O'Neill, past and present Wallabies, the Brumbies and NSW Waratahs squads as well as players from the Australian men's Sevens squad which he captained and the national women's Sevens squad he coached.
A host of his former Roosters teammates, including Chris Flannery, who flew back from England - where he plays in the Super League - also attended the service, as did NRL auditor Ian Schubert and judiciary panelist Royce Ayliffe, ex-teammates of Mackay's father.
On the coffin were draped seven jerseys for the teams he played with: Clovelly, Waverley, Sydney Roosters, Randwick, Melbourne Rebels, Australian 7's and the Brumbies.
Before playing for Randwick, the Waratahs and Brumbies, Mackay also spent several seasons in the NRL with the Roosters, fulfilling his dream to follow in the footsteps of his father John, who played for the club in the 1970s and '80s.
Mackay's younger brother Matt and lifelong friend and former Wallabies vice-captain Morgan Turinui delivered touching eulogies, while Father Nick Lucas spoke of the "profound influence'' the popular player had on so many others.
"He might not have had a full life, but it sounds to me he was full of life,'' Father Lucas said.
Mackay is survived by his father, mother Leonie, Matt and sister Kristy, who issued a family statement to express their gratitude to the Australian rugby community.
"Rugby was always a passion of Shawn's and the fact he was able to play professional football ensured that he lived and died a very happy man,'' the statement read.
"Shawn would have been humbled to have seen the tributes that were paid to him across the Super 14 competition over the weekend, and would have been extremely proud to see his Brumbies perform the way they did (with a win) against the Stormers.
"We were relieved to be able to communicate with Shawn how much we loved him and he to us.'
About 150 people attended a memorial service for Mackay at St Christopher's Cathedral in Canberra which was held simultaneously.
Reflecting on Mackay's life, former Brumbies coaching staff member Bob Hitchcock said he was, above all, a good bloke.
"Shawn Mackay was indeed a rugby journeyman whose dedication to the sport he loved was unquestioned and unwavering," Hitchcock said.
"For the game they play in heaven, the team has just got a lot stronger."
A group of around 50 boys from Mackay's Sydney high school Waverley College, who were in Canberra for a rugby training academy at the Australian Institute of Sport, formed a guard of honour outside the church following the service.
