Suffering from depression, with low self esteem and no confidence in himself, he weighed more than 25 stones and had tried and failed many times to lose weight.
Then he bought a pedometer and took part in a step challenge at work with Job Centre Plus and the missing piece of the puzzle clicked into place.
Now the 41-year-old has become a Mr Motivator to his colleagues, encouraging 120 people to take part in step challenges and charity fundraising events and is a gold winner in the Healthy Working Lives campaign run by NHS Greater Glasgow and Clyde.
This year he has set himself the target to sign up 1000 colleagues from Glasgow, Lanarkshire and East Dumbartonshire.
"I saw a picture of myself which shocked me to the core," he admits.
"I always knew I was heavy but I didn't realise how heavy. I was monstrous. I saw that picture and decided, enough is enough, I have to make changes."
He started by cutting out sugar and swapping pasta and bread for sweet potatoes, brown rice and lots of vegetables.
Then he started walking - and hasn't looked back. He was living in Clydebank at the time and walked the seven miles to work in Glasgow city centre every day.
For his first step challenge he encouraged six colleagues to take part and by the time he lost 10stones he had signed up 120 co-workers to join him in the step challenge and was writing regular blogs to keep everyone inspired.
"I discovered because I had lost so much weight I wanted to do more things. So I took up pilates, yoga and Thai boxing. Then I started running and I now run marathons and half marathons."
In a tie-in with Glasgow Life, Stephen now organises fitness boot camps for colleagues at Glasgow Green.
"About 60 of my colleagues signed up to do a weekly class, lifting tyres, climbing under nets, just to show there are fun ways you can be active."
He laughs: "When people at work see me coming they know there's something active coming their way."
Campaigning on health and obesity issues has given Stephen a positive focus in life. Now living in Glasgow with his partner Teresa - "She met the new me" - his life has completely turned around.
"If what I do can help one other person who is in the situation I was in make the changes necessary to become healthier, it has been worth it. Too often we hear people who are at the weight I was and they are told it's too late, you can't do anything and surgery is the only way forward.
"People with serious weight problems are frightened and continually told they are a drain on society and the NHS. I want them to feel better."
By getting active, members of staff at Greenock-based River Clyde Homes were motivated to raise money for charity as well as getting in shape.
They have climbed mountains to raise awareness and much-needed funds for cancer charities, competed in a pedometer challenges and organised boxercise classes and regular weight-ins.
Creating shower facilities at work and bike storage, as part of the Cycle to Work scheme, all encourage staff to keep active.
"Information communications support officer Stevie Kane says: "When I joined the company two years ago most of the experienced walkers went out with different groups. We found that we all wanted to get together and start up a club of like-minded folk.
"It snowballed from going one walk for a laugh to something more regular."
This year they have set their sights on walking Ben Nevis and it has encouraged people who had never exercised before to get out on the hills.
Lisa Buck, leader of the Healthy Working Lives team in greater Glasgow and Clyde, says the main aim of the project is to improve and protect the health of staff working in local companies.
All of the project's services are free to businesses and there are grants of up to £1000 available this year to cover costs for firms who want to get involved with Commonwealth Games-related ideas.
"In Glasgow we have about 250 companies who want to do an award with us," says Lisa. "They are the exemplar companies, so they will do the Healthy Working Lives award and have all agreed to work through different criteria to get this recognition.
"They will do regular activities and information campaigns, policy work that will change the environment of the workplace and can go from bronze to silver and gold awards."
Our Active 2014 campaign, with partners Glasgow Life and NHS Greater Glasgow and Clyde, is targeted at improving the health of Glaswegians in the year of the Commonwealth Games and building a lasting legacy of physical wellbeing.
Focusing on events and individuals of all ages, we aim to improve the health of as many people as possible in the community.
The positive message of this campaign is that even the smallest of changes in activity and lifestyle can make a huge improvement in health.
We will target a series of health goals, including basic fitness, obesity, diet and smoking cessation and deliver the message that small changes in activity and lifestyle can make a huge improvement in health.
We want to do all this by raising the profile of health and fitness initiatives and opportunities.