Charlotte Caldwell, the mother of Billy Caldwell, led a campaign to get the law changed so that thousands of other children could benefit.
Sajid Javid has announced that senior doctors will be able to prescribe cannabis-based medicines in the UK later this year after the government agreed to ease the ban.
Ms Caldwell said she was impressed by the speed at which Mr Javid had acted.
She said: “It’s absolutely incredible, it’s amazing. The compassion and speed that the Home Secretary has moved with is just incredible.
“The Home Secretary is King of Hearts, not just for Billy, but all the children and people who have suffered because they could not get this medication.”
She said the news was the perfect birthday present for Billy who turned 13 on Thursday and received his possession licence which means his cannabis medication can now be administered.
Ms Caldwell had attempted to bring in medicinal cannabis oil to the UK but it was confiscated at Heathrow after a flight from Canada.
She said many children and people will benefit from the government’s change of stance on cannabis medication.
“It’s going to be a huge step forward for a lot of these children throughout the UK who can now have the treatment they need,” she said.
Ms Caldwell added: “There is a lot of confusion over the different products that have to be prescribed. It needs to be moved to the health department and it needs to be explained to people how this is going to work.”
The government’s medical adviser Professor Dame Sally Davies conducted a review and concluded there is evidence that medicinal cannabis is effective.
The Department for Health and Social Care and the Medicines and Health Products Regulatory Agency (MHRA) will now develop a clear definition of what constitutes a cannabis-based medicine.
Specialist clinicians will be able to prescribe products that meet safety and quality standards by the autumn.