Tracy Spicer-Neal, aged 49 from Wolverhampton, trekked up the 164ft high building in aid of Macmillan Cancer Support.
She lost her mother Sandra to breast cancer during the coronavirus pandemic. Her grandmother also died of breast cancer.
Tracy completed the challenge on August 11 and has raised more than £800 to date.
The idea to climb the O2 began in 2015 when Tracy and Sandra visited the attraction as part of an Elvis exhibition.
She said: "When we got there, we noticed people were climbing up the building and mom turned to me and said she really wanted to do it.
"So, on August 11, I did it. Once I got to the top, I raised a toast to my mum. After the day, I am completely tired and blisters on the balls of my feet."
She added: "I chose Macmillan because mom used to support Macmillan with a monthly donation."
Jayna Kawa, fundraising manager for the charity, said: "It seems that fundraising for charity runs in the blood of Tracy and Sandra.
"I’ve heard that Sandra often used to support local charities doing things like, dressing up and participating in annual sponsored walks and now Tracy is now picking up the baton.
"We couldn’t be more grateful to Tracy for choosing Macmillan and we really hope she has a head for heights.
"The money raised will help us to fund more healthcare professionals in local hospitals. Thank you, Tracy."
To donate to Tracy's fundraising page, visit www.justgiving.com.
To contact Macmillan Cancer Support, call 08088080000 from Monday to Sunday, between 8am to 8pm.