Nearly 25 years after losing his first child, Neville Lawrence, 76, said the decision was the hardest he has ever made, and that he struggles to put into words the devastation caused to his family when his son was killed.
Stephen was murdered by a gang of racists in Eltham, south-east London, on April 22 1993 at the age of 18.
His father told the Press Association: "The fact that I had to lose my first child has been devastating. I can't begin to explain the pain and the anguish me and my family have suffered over the past 25 years."
He plans to spend the 25th anniversary of his son's death in church.
Two of the group of up to six thugs who attacked the teenager and his friend Duwayne Brooks, simply because they were black, have been convicted of murder, but the rest have evaded justice.
David Norris and Gary Dobson are both serving life sentences, while three other men who have consistently been accused of the killing but never convicted are Jamie Acourt, 41, from Bexley; his brother Neil Acourt, 42, who uses his mother's maiden name Stuart, and Luke Knight, 41, both from Eltham.
The initial investigation into Stephen's death was hampered by incompetence, racism and alleged corruption.
A key moment was when Mr Lawrence and his ex-wife Doreen met Nelson Mandela two weeks after Stephen died.
"When I met him for the first time I was so inspired by his persona and the way he talked to people," Mr Lawrence said.
"He made it clear to us that in his country it was something that they go through every day, but never in his wildest dreams did he think that something like that would happen in a place like Britain.
"Meeting him gave me the courage to do some of the things I have done over the years.
"Other families came to my rescue as well. When you are going to go on a journey, if somebody else who has been through it comes and talks to you they can give you an idea what you're going to face down the road.
"What those families did for me I can't even start to explain to people. I decided, after a certain amount of time, on my journey, that if anybody who had the same kind of experience wanted me to come and talk to them then I would do that.
"I also decided that I would go into schools and universities and talk to the younger generation."
Parts of the UK, particularly London, have seen a surge in violent crime in recent months, with nearly 60 murders in the capital so far this year.
Mr Lawrence, who speaks to young people to spell out the dire consequences of carrying a weapon, said: "Right now with the violence, and the knife crime violence, it is even more urgent now that I talk to these youngsters and explain to them the pain and the suffering they inflict on families.
"It is a life sentence and something that will never be served. I've been serving a life sentence for the last 25 years and I will go on serving that until the day I die."
He believes if young people are left with nothing to do they will get involved in activities that are "devastating" to the community in which they live.
Mr Lawrence and his former wife, who is now Baroness Lawrence, have campaigned for more than two decades to get justice for their son.
The botched case led to a major public inquiry and eventually a change in the law to allow Dobson to be tried twice for murder.
Detectives have admitted their investigation is unlikely to progress without new information.
But the case remains under scrutiny with an inquiry into undercover policing examining claims that police moles infiltrated campaign groups supporting the Lawrence family.
Mr Lawrence's solicitor Jocelyn Cockburn from Hodge Jones and Allen said: "I am humbled by his message of forgiveness to mark the anniversary of his son's death.
"Neville can feel proud of what he has achieved in the intervening years."
Former plasterer and decorator Mr Lawrence believes that in death his aspiring architect son has become a "legend".
He said: "When these boys killed my son Stephen, they created a legend. In his death, Stephen is a legend.
"There is debate about racism, there are organisations set up to help to make people understand about racism, the police have been put under the spotlight because of Stephen's death."
The father-of-three and his family, who have fought with immense dignity despite scandalously poor treatment by the police, will never escape the pain of what happened.
He said: "My family, especially me, I will never be the person I was before Stephen's death.
"Maybe sometimes people think you can just brush things aside. You can never brush this aside, this is going to live with you for the rest of your life.
"This is a life sentence that you can't finish. The only time my life sentence will be finished is when I'm in the ground."
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