The 39-year-old actress opened up for the first time about the death of her close friend who died in March after a freak skiing accident at a Canadian resort in the July issue of Harper's Bazaar U.K.
"She would have a plan on arrival anywhere and would be carving the best out of life and every situation and every person," Thurman told the magazine as reported by Fox News.
"She wasn't as much a passenger as I am, which made us great companions in life ... because every driver needs a passenger ... and every passenger needs a driver. So it's a big loss in my life."
Richardson, the wife of actor Liam Neeson, co-starred with Thurman in the 2001 film Chelsea Wall.
A heartbroken and bleary-eyed Thurman was photographed at Natasha's wake in New York City and again in the tiny upstate New York town where she attended Richardson's funeral service.
Natasha's loss has allowed Thurman to realize that she needs to fully embrace life, she said. For now, the "Kill Bill" actress is planning a London wedding to British philanthropist Arki Busson.
"Isn't life amazing? Isn't life full of surprises? When it comes to things like marriage, you just never know," she said. "I find that growing up has been all about realizing that life gets more serious, and that it's also really important to increase your sense of humor."