The commercial appeal of the Premier League giants means they can do separate sponsorship deals for their training kit and the famous red shirts they play in.
It is the first time United have sold naming rights to their training ground in Carrington on the outskirts of Manchester in northern England.
The facility will be called the Aon Training Complex under the agreement that begins in July.
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The Aon brand is already on the United playing kit but it was previously announced the name will be replaced by Chevrolet from 2014 after United signed a record $559 million (£365 million), seven-year deal with US carmaker General Motors.
"I am delighted this cements our relationship with Aon for a further eight years," said United commercial director Richard Arnold in a statement.
Financial terms of the new agreement with Aon, the world's largest insurance broker, were not disclosed.
Based on the value of previous deals, it can be calculated the new agreement is worth up to $30 million (£19.5 million) per annum for United.
Logistics company DHL has been paying United around £10 million a year to sponsor the training kit.
The club negotiated an early conclusion to that contract at the end of this season in order to find a more lucrative deal.
United, owned by the American Glazer family, look set to win the top-flight title for a record 20th time this season. They have a virtually unassailable 15-point lead over second-placed Manchester City ahead of Monday's derby between the two teams.
Keen to reassure fans worried about the extent of the club's commercial ambitions, United said there were no plans to seek a sponsor for their stadium.
"Old Trafford will not be sold," executive vice-chairman Ed Woodward said, referring to naming rights for the club's home.
A vocal group of fans have criticised the Glazers for loading the club with debt after a £790 million takeover in 2005.
However, United's renewed success on the field this season has helped to mute those protests.
Aon, which is listed on the stock market in New York, has its global headquarters in London and operates in 120 countries.
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