Caroline Jones, 47, from Harpenden in Hertfordshire, began Knickers Model's Own in memory of her mother Mary Benson, who died of breast cancer.
She has raised £36,500 - or £100 a day - and donations are still coming in.
"It's incredible... [this amount] could fund two PhD students for a year," she said.
"This is a very happy day for me, the target felt hugely ambitious but we've done it and this money continues the pioneering work at Cancer Research UK, in the fight against cancer.
"The campaign runs until 31 December and the fundraising is open-ended, people can always donate... who knows where it will finish."
Mrs Benson, who died in October 2014, had been a volunteer at the charity's Harpenden shop for 13 years.
Mother-of-three Ms Jones started volunteering as a window dresser soon after her mother died and on New Year's Eve last year decided she would post a photograph every day on social media of her wearing a different outfit.
She hoped to raise £1,000 in a year, but her daily posts became so popular she increased her fundraising target.
A sale of about 1,000 items of clothing and accessories in November raised just over £2,600.
She celebrated the news or reaching her target by announcing her next project will be writing a book about her year of pre-loved fashion.
"I won't be bored, I'm not going anywhere," she said.
A woman wearing charity shop outfits every day this year to raise money for cancer research, has reached her target three weeks early.