The civil servant, 62, died last October, 18 days after he was punched and kicked in a homophobic attack in central London.
His sister Jenny said she missed him “dreadfully” and called on the public to “take responsibility” for reporting such crimes.
Describing her brother as her “protector”, she said: “He was very generous. He loved people. He had this great knack of engaging people.
“My younger brother and I used to say that he really was a must at any party because he loved it. He got on well with everybody.”
Ms Baynham, 59, condemned the homophobic abuse hurled at him on the night of the attack and said that their 89-year-old mother Muriel had been left “desperately upset” by his death.
Mr Baynham was killed while out celebrating a new job at the Foreign Office.
After the attack, he was taken to the Royal London Hospital, where he died from a brain injury 18 days later.
Ms Baynham said: “I went to the hospital nearly every day and when I first saw Ian I looked at him and I thought ‘I can’t see how you are going to survive’.
“He looked so ill. The hospital staff were fantastic. They did everything they could but he never responded, probably from when he was rendered unconscious. That was the last time he knew any life, I think.”
She stayed at his bedside with his close friend George Richardson, 53.
Mr Richardson said: “You spend 18 days hoping for some kind of miracle. But when I saw the medical staff on the night he was admitted, they told me how very poorly he was.”
Ms Baynham said she and Mr Richardson were both holding her brother’s hand when he died.
“I said to George ‘I think he’s slipping away’ so we were left and we were with him, which was quite important to us.”
Ms Baynham said she was angry at hearing that her brother had been called anti-gay slurs before he was attacked.
She said: “I can’t believe it. That makes me angry to hear that. I am not normally angry but I just feel it’s so wrong, it should never be. We shouldn’t be able to treat each other like that – something about dignity and respect.
“It doesn’t matter who you are, we should be able to give that to everyone, whoever we come across.”
She added: “I do believe that we do need to do something about any sort of abuse to anybody. It is just not acceptable but it is particularly tragic because it is so close.
“I thought that we had moved on a long way and I am really surprised that this sort of thing is still thrown up and is still an issue.
“But I think that it is the general public’s responsibility to do something about that and report more of these sorts of incidents.
“There is still a huge prejudice relating to homophobia.
“I have seen that not only in this country but also in Australia and I think a lot more needs to be done.
“I don’t think there is an easy answer to it and I think as individuals everybody has certain feelings about different sections of society but it is about tolerance, that is important.”
She said she hoped “something positive” would come out of what happened.
Mr Richardson said he was “probably not as shocked and surprised” about the nature of the attack “because you know how much of it goes on”.
“You know how much of it in the past has been under-reported, and I hope more people are prepared to come forward now,” he said.