The 18-year-old made the announcement on Friday as she spoke at a 'Homecoming Party' staged by the Lawn Tennis Association at the National Tennis Centre in London.
Earlier she had played tennis with the Duchess of Cambridge, who is a patron of the LTA.
Richardson, who was born in Peterborough and grew up in Bourne, was hired as coach for Raducanu's summer tournaments in the United States.
That stint ended with the teenager's sensational US Open win at Flushing Meadow, where she claimed the title without dropping a set in the entire tournament..
Raducanu had entered the tournament as a qualifier, and the world number 150. She is now on the brink of the world's top 20.
At the time of her success in New York at the beginning of September, Raducanu said of Richardson: “He’s been good at instilling the fundamentals into my game and making me realise that doing the basics to a really good level is going to take you a long way.
“He’s also a very calming character. He’s good at relaxing and reassuring me. if I get too hard on myself.”
But today she revealed she is on the lookout for a new coach after announcing a split with Richardson.
"At this stage of my career I really need someone that has had that WTA Tour experience at that high level," said Raducanu.
"Especially right now as I'm so new to it, I think I really need someone just to guide me who has already been through that themselves.
"Never did I even dream of winning the US Open and now I'm ranked 22 in the world, which is pretty crazy to me."
Richardson had only taken over as Raducanu’s coach after her run to the fourth round at Wimbledon earlier this year.
The 47-year-old has done little coaching at main tour level, but worked with Raducanu when she was 11 at Bromley Tennis Centre.
As a player, Richardson reached the third round of the singles at Wimbledon, the Australian Open and the US Open.
He won five Challenger Tour men’s doubles titles, one with Tim Henman. He was best man at Henman’s wedding.