Chris (29) said earlier he never thought he would wear capping regalia again after accepting his own degree, let alone wear it on behalf of his sister.
Sophie Kate Elliott (22) was killed in her parents' Ravensbourne home on January 9.
On Saturday, she would have received a first-class honours degree in economics at the graduation ceremony.
"It is a sad day.
''I wish she could be here to get the degree herself," Mr Elliot said before the ceremony.
It is the first time a posthumous degree has been awarded "in person" in the university's 140-year history.
The family was initially offered a private ceremony, but was grateful for the university's response in allowing the degree to be conferred during the main ceremony.
Father Gil Elliott said he knew his daughter had worked hard for her degree and would have travelled down from the job she was to take at the Treasury, in Wellington, to accept it in person.
"I guess we knew she worked hard for years to get her degree and just because she isn't with us anymore doesn't mean she shouldn't be part of the ceremony."
Lesley Elliott said her daughter's friends were at the ceremony, some receiving degrees.
She said the day would have been greeted with great excitement by her daughter.
"She would have been having a ball, and no doubt stressing us all out," she said.
Gil Elliott said the day was full of mixed emotions for the family.
"It is a bittersweet thing," he said.
"We are really proud of [Chris], of course, and we are really thankful to the university."
