Charlotte Caldwell said they had "achieved the impossible" after Home Secretary Sajid Javid announced on Saturday he would grant a licence for 12-year-old Billy to get the treatment.
-> The little known medical conditions which could land you a £1,000 fine behind the wheelThe Government, however, only relented after a six-day battle ensued when officials seized a six-month supply of cannabis oil she brought into Heathrow Airport from Toronto, Canada.
She criticised the "dreadful, horrific, cruel experience" that has deeply affected 12-year-old Billy, saying: "His little body has been completely broken and his little mind."
"I truly believe that somewhere in the Home Office there's someone with a heart and I truly believe that Billy was pulling on their heart strings," she added.
She criticised outdated laws and called for "more humane policies", while vowing to fight for others in the UK to have access to the medication they need.
"No other family should have to go through this sort of ordeal, travelling half way round the world to get medication which should be freely available," she said.
"My experience leaves me in no doubt that the Home Office can no longer play a role in the administration of medication for sick children in our country."
Mr Javid said he has used "an exceptional power" to "urgently issue" a licence to treat Billy with cannabis oil.
-> Car caught travelling the wrong way down West Yorkshire motorway junction"This is a very complex situation, but our immediate priority is making sure Billy receives the most effective treatment possible in a safe way," he added.
"We have been in close contact with Billy's medical team overnight and my decision is based on the advice of senior clinicians who have made clear this is a medical emergency."
On Monday, Border Force officials confiscated the supply of the medication used to treat Billy for up to 100 seizures a day after Ms Caldwell, 50, flew with it into the UK airport.
Ms Caldwell, from Castlederg, Co Tyrone, Northern Ireland, went on to accuse Policing Minister Nick Hurd of having "likely signed my son's death warrant" ahead of a meeting.
On Saturday, she said that since medication had run out the boy's seizures had intensified, pushing him into a "crisis situation".
But after she and her team worked through the night with the Home Office, the medication was making its way to London's Chelsea and Westminster Hospital, where Billy is being treated.
Ms Caldwell credits the oil with keeping the boy's seizures at bay, saying he was seizure-free for more than 300 days while using it.
Billy started the treatment in 2016 in the US, where medical marijuana is legal.
He became the first person in the UK to receive a prescription after his local GP in Northern Ireland, Brendan O'Hare, began writing scripts.
But Dr O'Hare was summoned to a meeting with Home Office officials recently and told to stop.