It will oversee press office functions, corporate and b2b comms and help support events for the power generation firm.
Phil Watts, head of group marketing at Aggreko, explained why Grayling was awarded the account, ahead of three companies.
He said: "It was Grayling’s global reach, knowledge and skills in our core business sectors and the personalities of its communication team that swung our decision in its favour."
The international trade comms brief was issued after a shake-up at Aggreko last year that saw the creation of three regional units - Europe, the Middle East and Africa (EMEA), Asia, Pacific and Australia (APAC) and the Americas.
Watts added: "Following our restructuring the company didn’t have a PR agency to engage with the media on our core sectors of international mining, oil and gas, utilities and events."
Some of the events Grayling will provide press support for this year include Investing in Africa Mining Indaba in Cape Town this February and the FIFA World Cup in Brazil.
The account team is spread across offices in Edinburgh, London and Dubai and will be led by Billy Partridge, director of Grayling Scotland.