Honor Smith, nine, had written to Branson to thank him for sharing a video that showed dyslexia in a positive light.
Branson shared the video above, which was created by 12-year-old girl called Isley, on his Virgin blog, in May 2015,.
Smith wrote in her letter that the video made her feel more "confident" at school.
Branson has posted her touching handwritten letter on his Virgin blog post, as well as the response he sent back.
He wrote on the blog: "Having recently shared 12-year-old Isley's inspiring story about dyslexia, I was delighted to receive a letter from young Honor Smith, a nine-year-old girl who has the condition."
Smith, who dated the letter 4 June, thanked Branson and wrote: "When my parents told me I had dyslexia, I thought my life was ruined but I watched your videos on it!
"So thanks, I really appreciated it!"
Because of the time Smith took to write him a letter, Branson decided to sit down with a pen and paper to reply, as he said it was so "nice" to receive a handwritten note.
In his reply, Branson wrote: "I am really glad you enjoyed the videos on dyslexia.
"Don't ever let people put you down for being dyslexic. Being dyslexic is actually an advantage and has helped me greatly in life.
"I look forward to hearing what great things to achieve in the years to come.
"Best wishes to you and good luck for the future, love Richard and all the family."
The Virgin founder tweeted out his blog post showing the handwritten notes to his 5.83 million followers.
One teacher tweeted: "You inspire so many children living with the gift of dyslexia. You and children with dyslexia inspire me to be a better teacher."
Isn't he just great?
Click through the gallery below to see more famous people who have dyslexia: