The Conservative Party Conference in Manchester in October is expected to generate £27.4m for the local economy, according to Marketing Manchester.
The agency, which is responsible for attracting conferences to the city, said the conference will be the largest economic impact of a political party conference held in Manchester since the city established itself on the circuit back in 2004.
The conference will take place 2 to 5 October at Manchester Central and is expected to attract around 13,000 delegates to the city.
The announcement follows The Mersey Partnership's predictions that the Labour Party Conference taking place in Liverpool in September is expected to boost the city's economy by £15m.
Andrew Stokes, chief executive of Marketing Manchester, said: "Political party conferences have been one of the city's biggest success stories of the last decade.
"The development of Petersfield, investment in the surrounding infrastructure and a city-wide partnership approach has enabled us to not only attract these events but keep them coming back year after year.
"They are now a firm fixture of the city's business tourism calendar and contribute a significant amount to the city's £573m-a-year conference industry."
Baroness Warsi, Conservative Party co-chairman, added: "I was very impressed with Manchester as a host city, and particularly Manchester Central as a Conference venue, when we first came in 2009. Manchester rightly deserves its reputation as a first class conference destination."
Marketing Manchester said the economic impact of business tourism events is calculated using a VisitBritain formula that takes into account corporate and individual spend across the event.
The city was first used as a party conference destination in March 2004 with the Labour Party spring conference. Since then, the city has seen three Labour party annual conferences in 2006, 2008 and 2010 and its leadership election of 2007. The Conservative party held its first conference in Manchester for over 100 years in 2009.