They first appered in the 1967 story "The Macra Terror" in which their home planet was colonised by humans but the Macra took control of the colony and hypnotised the humans into mining gases for them. They were defeated when the Second Doctor effected an uprising on the planet and destroyed the control centre with an explosion, killing the Macra in charge and apparently dooming the Macra on the planet.
They later reappeared over 40 years later in the 2007 episode "Gridlock." Over the coarse of billions of years, The Macra devolved into feral beasts that survived on New Earth, by feeding on the poisonous fumes and stray people who came down in their cars to the "Fast Lane" of the Motorway in New New York. They were apparently again doomed when by 5,000,000,053, the Tenth Doctor opened the roof of the Motorway, allowing the cars to escape to the Upper City, depriving the Macra of food and gases. The Macra presumably died off due to lack of sustenance.