The horse-powered Dundee Corporation tram dates from the late 19th Century and is believed to be one of the first built for the city in 1887.
It has now been removed and taken to Dundee Transport Museum to be restored and added to the collection.
The museum already has the last surviving Aberdeen tram.
The Dundee tram was removed from service to be replaced by electric vehicles shortly after the turn of the century.
Almost all the old trams were burned, but the number 24, which ran a route through Dundee city centre in to the west end, survived.
It was transported to Perth where it was placed in the garden of a man called Jock Ness.
Jimmy McDonnell, chairman of Dundee Museum of Transport, said: "It's one of the first built for Dundee and is almost certainly the last of its type to survive - and it's one of the oldest surviving in Scotland.
"It has now lain in that garden for a long period of time - we can account for at least 60 years, but we believe it has been there for up to 100.
"It has been used as a summer house, but it still has its original interior which is astounding."
"When we found it in situ it was just about landlocked - the houses and an orchard have grown up around it."
Mr McDonnell and a team of volunteers, including heavy moving experts, worked to lift the tram and transport it to Dundee.
He added: "It weighed two tons and we had to lay a plastic road and get it on to a low loader with special lifting plant.
"We have people coming up from the British National Tram Museum to take a look at it because they are very interested in it.
"It will take pride of place in our museum when it is restored."
What is thought to be the last surviving Dundee tram has been found in a garden in Perth where it was being used as a summer house.