The 31-year-old lost his beloved mum Mish to kidney disease last year, at the age of 67.
She had waited three years for a transplant.
Stefan praised the Evening Times for our campaign for an opt-out system of organ donation, where the default position is that everyone is a donor.
Like major charities including Kidney Research UK, the British Heart Foundation and the Cystic Fibrosis Trust, he believes it is the best way to make more organs available, and ultimately save lives.
Labour MSP Drew Smith is preparing to launch a Bill at the Scottish Parliament calling for a change in the law on the back of our Opt for Life campaign.
Stefan, who has just finished a run of the hit musical Chicago in Glasgow, said: "I think it's a fabulous thing that you are doing. I'm fully in support of it and I'm very impressed that the Evening Times has been so pro-active on it.
"Everyone has got their own story but, for me, I became conscious of the issue from a personal point of view. My mum's kidney transplant bought her time but it happened too late.
"If there had been more organs available she would have got a donor kidney quicker.
"It's a fabulous thing to be on the organ donor register and an opt-out system is something people should really push for."
Mish lost her fight for life in May last year after three decades of illness.
She suffered from autosomal dominant polycystic kidney disease, an incurable condition which has also affected his siblings, Tammy, 42, and Damian, 40, but not Stefan.
Mish's father, Brigadier Reginald Harrison OBE, died of the same disease, when he was 57.
Stefan's mum was diagnosed with ADPKD, which causes multiple cysts to develop on the kidneys, during her first pregnancy.
Despite the fact that abnormal kidney develop-ment is thought to start soon after birth, symptoms – which include high blood pressure (hypertension), abdominal pain and blood in the urine – tend not to begin until adulthood, when the disease is already advanced.
ADPKD affects one in 1000 people and is the most common genetic condition to affect the kidneys.
Progressive damage to the kidneys results in organ failure in almost all patients. At this point, dialysis – treatment that involves machines that replicate many of the kidney's functions – or a transplant are needed or the patient will die.
Around 90% of people waiting for a transplant are in need of a new kidney.
Stefan said: "Kidney disease is a silent killer. There are 3million people at risk of total kidney failure in the UK and 1m are yet to identify it.
"And 50,000 of those 2m are in all-out kidney failure.
"Although organ donation is not going to fix the problem, it buys them time while research work is carried out."
The actor, who played Greg Jessop in the hit soap and also starred in Hollyoaks, lives in London with his wife Debbie, 35, daughter Tabitha, three, and son Benjamin, one. He was made an Ambassador for the charity Kidney Research UK, last year, shortly before his mum passed away.
The charity has been a vociferous supporter of our Opt for Life campaign.
Stefan said: "Kidney Research UK is not a charity that is government funded in the same way as the major charities.
"They have to turn away four out of five research projects because of a lack of funding. But the projects that they are involved with are ground breaking.
"I'm an avid campaigner for them. It's been an incredible privilege to watch some of the projects that are going on.
"It goes as far as stem cell research and taking cells that heal and regenerate parts of the body.
"I've had the chance to see the future of modern medicine and what's going to be happening in the next 20 years. One day they will may be able to inject stem cells into the right area and it will heal the problem.
"It's not something for our generation but certainly for our children and our children's children."
Wales is preparing to launch an opt-out system in 2015 and Stefan hopes the rest of the UK will follow suit.
"The UK is a progressive nation. It makes a lot of sense for us to get behind this," he said.
For more information about kidney disease go to www.kidneyresearchuk.org