He was a World Cup final winner against France in Cardiff in 1999 and runner-up four years later against England in Sydney, when Jonny Wilkinson's drop goal stunned the Wallabies.
Larkham had been considering a number of offers in France and England, but when he leaves the CA Brumbies it will be Scotland's capital which beckons, having agreed a two-year deal.
He said: "It adds a bit of security knowing I won't have to mess around with contract negotiations during the World Cup and gives me a greater opportunity to focus on what needs to be achieved.
"I have always been focused on getting to the World Cup and for me ending on a winning note would be very special."
The fly-half, capped 95 times by his country, has stressed the importance of the upcoming two Tests against Wales, especially as the two teams are drawn in the same pool at the World Cup.
Many Australian rugby fans were disappointed when it was announced the Welsh would leave 18 of their best players behind in the UK to attend a summer fitness camp ahead of the World Cup.
But Larkham has dismissed the make-up of the side as a side issue, arguing it is their style of play which will be important.
Larkham added: "The Tests (against Wales and Fiji) leading up until the Tri-Nations is a good opportunity to work on our execution and build as a team and is an excellent opportunity to experiment with certain positions."