Fountain, 35, shared on Instagram: "I DID IT!!!!!!!
"From having a stroke in august to running a sub 4 hour marathon. I am beyond proud of myself. THANKYOU to everyone who cheered, donated, ran with me and everything else in between. I’m so, so happy. Will never forget this feeling. #teamstroke #londonmarathon #sub4hours #running "
The actor - who came second on Dancing On Ice in 2008 - was just 34 when he suffered a mini-stroke that could have killed him if it had not been diagnosed in time.
Fountain revealed he was treated in hospital when he woke up feeling strange and dialled 111 after calling his mother and finding it difficult to speak.
He said: “I called 111 on my mum’s advice and they sent an ambulance for me, it was so scary.
“I felt stupid because I knew exactly what I wanted to say to the doctors, but I couldn’t get the words out, I was speaking like a toddler, I was really embarrassed."
Fountain was admitted to Homerton University Hospital in August 2022 and transferred to a specialist stroke unit at The Royal London Hospital.
Doctors diagnosed a Transient Ischaemic Attack (TIA), also known as a mini-stroke, caused by a blood clot on the brain, which Fountain described as a "ticking time bomb in my head".
The actor suffered damage to the left side of his brain and is has been working with a speech therapist to regain 90 per cent of his speech.
Fountain rose to fame as Justin Burton in Hollyoaks between 2003 and 2009.
He then became known for playing Jack Duckworth's grandson Tommy Duckworth in Corrie in 2010.
But he was sacked from the ITV soap in 2013 after he was revealed to be have recorded a YouTube video rapping about violence against women.
He said afterwards: "I let a lot of people down including myself. I didn’t leave the house for a long time, I was really depressed and really ashamed and rightly so."
Watch: Chris Fountain discusses suffering a mini-stroke aged 34