The company has been the club's shirt sponsor since 2009, but will be replaced by General Motors-owned car brand Chevrolet from 2014 as part of a record $559m (£365m), seven-year deal.
In an effort to retain links with Manchester United and its growing fanbase across Asia, the new deal will involve the club's training facilities at Carrington being renamed the Aon Training Complex.
Aon will also replace DHL as the training kit sponsor. Manchester United became the first Premier League club to separate the sponsorship for its playing and training shirts in 2010.
Phil Clement, global chief marketing and communications officer at Aon, said: ""The first phase of our relationship brought Aon an explosion in brand awareness.
"This phase of our partnership is a more holistic approach where we can use our expertise and create a global dialogue and knowledge share around the fields of talent, healthcare, risk, retirement, and data and analytics to help deliver great performance and great results."
The company will also become presenting partner for all Manchester United pre-season tours over the coming eight seasons, including trips this year to Bangkok, Sydney, Yokohama, Osaka and Hong Kong.
To read a full list of Manchester United's global sponsors, read our analysis on the rising price of admission to football sponsorship.Follow @alex_brownsell