It was the speech that moved a room of Sydney's most powerful people to tears.

Stuart Kelly, the brother of 18-year-old "one punch" victim Thomas Kelly, has revealed the moment he and his family learned their beloved Tom was on life support at St Vincent's Hospital following an attack by an intoxicated stranger in Kings Cross on July 7, 2012.

Speaking at the Take Kare gala dinner to raise money for the Thomas Kelly foundation, Stuart addressed an audience of more than 700 people, including Premier Mike Baird, Lord Mayor Clover Moore, the Prime Minister's wife, Lucy Turnbull, and NSW Police Commissioner Andrew Scipione.

Stuart maintained his composure, unlike most of the audience, as he called on Mr Baird to maintain the state government's hardline lockout laws to prevent any more senseless violence affecting families like his own.

"I look back at that moment: I was 14 years old, I was told by a stranger that my brother, my best friend, was going to die. Those few words would change my life forever.

"I'm now 17 - that was three years ago. However I carry a deep scar that you cannot see. It's always there, it never leaves. It sits below the surface of your skin and surfaces when you least expect it."

He continued: "[We need] change to stop the growing epidemic of drug and alcohol abuse, and misuse, and to say no to senseless violence.

"Premier, will you make this promise tonight?"

Earlier, Mr Baird had applauded the work of his predecessor Barry O'Farrell in instituting the changes that have resulted in a dramatic drop in violence in the Kings Cross area following a raft of law changes.

Stuart Kelly's speech to the Take Kare gala dinner

My name is Stuart Kelly, I'm Thomas' younger brother. I was 14 years old when Thomas was brutally attacked without reason; resulting in him losing his life.

Tom was out with his friends, it was his first night out in Sydney. We were at home in Bowral, doing what many families do on a Saturday - watching TV and getting ready for bed.

The phone rang at 10.25pm. Mum answered it but couldn't comprehend what the person was telling her, so she passed it to dad. The voice on the end of the phone told them that they needed to come to St Vincent's Hospital urgently.

Mum and dad told my sister, Madeline and I, that Tom had been in an altercation; they had to drive up to Sydney to be with him but would probably be back later during the night.

We had absolutely no idea about the extent of Tom's injuries. The person from the hospital did not give any further information, except to firmly ask that we come straight to the hospital.

Maddie and I stayed at home. It was really late, so we went to bed. On Sunday morning, mum's sister Carrie called, telling us that she was driving down to Bowral from Sydney to pick us both up. I felt really uneasy, I couldn't understand why Carrie would be coming and not our parents.

Later at home I thought what might have happened to Tom. Never did I think or imagine that we might lose our brother.

I remember walking into the floor at St Vincent's hospital, around midday on that Sunday – the floor was bustling with people. As we made our way to the lifts, I tried to work out what was going on and why we were there. Madelaine had even brought her school books with her to study because she was stressed about her upcoming HSC trial examinations.

We took the lift to the fourth floor, where mum and dad met us. They took us into a small room, closing it … closing the door. I could tell by the look on their faces that something serious had happened. I thought this was really strange as we were not visiting Tom – nothing was making any sense to me.

Finally dad said to us, "Thomas has been badly hurt, the doctors want to explain it to the both of you". I felt uneasy. We waited what seemed to be a very long time, but probably wasn't. Two doctors came in with a social worker. We all sat down. I was feeling scared and anxious, and I was about to find out why.

"Your brother Thomas is in a critical condition and will not survive".

I was being told to prepare for his death. Those few words would change our lives forever. I don't remember too much more of what they said. I was in shock and total disbelief. I heard those terrible words but was feeling that this could not be real, this could not be happening to Tom. I could not process this as a reality.

I look back at that moment: I was 14 years old, I was told by a stranger that my brother, my best friend, was going to die.

I'm now 17 - that was three years ago. However, I carry a deep scar that you cannot see. It's always there, never leaves. It's just below the surface of your skin, and surfaces when you least expect it.

The last time that I had seen Tom alive was at a Wallabies game against Wales on the 23rd of June. We had so much fun, lots of banter between the two of us, laughing at the Welsh accents – trying to imitate them. It was a great afternoon, but now it is a memory caught in time, a memory of my final time with Tom. It is a memory which should continue to be joined by many more, as we grow up and grow old together.

Tom never deserved to die that night, it was not meant to be his time. In fact, I believe now that it could and should have been avoided. Our family lost a son and a brother.

I ask all of you to look at me, I am but one person who has been affected by violence. It is a sentence that I have to carry for the rest of my life. My mother, father and sister now carry this sentence. Our relatives and friends, Tom's friends, carry this sentence.

We are not alone, there are many many thousands of other who are directly affected by senseless violence every year. Today, I am preparing to complete Year 12 at the King's School, with my HSC only weeks away. My graduation is this Friday.

I still remember sitting in the hall with my parents and Madeline, watching Tom graduate. Now it's my turn. How will I feel when the headmaster shakes my hand?

I want to ask all of you in this room right now to think of your children, or the children of someone special that you may know. Would you want them to be here on this stage now making this speech? It's time for change. Action is needed through strong leadership from the NSW state government and the federal government. Action is needed by our friends and our families across all of our communities - change to stop the growing epidemic of drug and alcohol abuse and misuse that is turning now into senseless violence.

Premier will you make this promise tonight? Australia is an alcoholic; we need to rethink the way we drink. Tonight your involvement and your voice can and will make a difference. To finish I would like to read a short poem that my father read at Thomas' funeral. It is a stark, blunt message to us all, it started with 'The Guy in the Glass':

"When you get what you want in your struggle for pelf,

And the world makes you King for a day,

Then go to the mirror and look at yourself,

And see what that man has to say.

For it isn't your Father, or Mother, or Wife,

Who judgement upon you must pass.

But the man whose verdict counts most in your life

Is the man staring back from the glass.

He's the feller to please, never mind all the rest,

For he's with you right up to the end,

And you've passed your most difficult test

If the man in the glass is your friend.

You may be like Jack Horner and 'chisel' a plum,

And think you're a wonderful guy,

But the man in the glass says you're only a bum

If you can't look him straight in the eye.

You can fool the whole world down the highway of years,

And get pats on the back as you pass,

But your final reward will be heartaches and tears

If you've cheated the guy in the glass."

Thank you.