"Joel is in there today - I don't any of us could imagine what that would be like and I said to him that the city was very proud of him," Mr Baird told journalists in Martin Place.
"Proud of him being able to be strong in spite of what he went through and that's very clear the thoughts in relation to [victims] Tori [Johnson] and Katrina [Dawson] are strong in there.
"There's a strong sense of comradeship that says we can get through this together, we are stronger together, just as the city has marched forward today."
Two plaques will be unveiled at the store on Friday to commemorate the lives of Mr Johnson and Ms Dawson.
Lindt Australia chief executive Steve Loane said the store reopening came after "three months of sadness".
He said the company was committed to making "today a happy day to celebrate that we're back and we're open with the support of all the staff".
"But really they're in a great mood and they're ready to go, and they really want to welcome customers in," Mr Loane told ABC Radio on Friday.
Regular trading hours begin on Saturday.
Mr Loane said Mr Johnson's plaque contained the image of a sunflower and Ms Dawson's the image of a tree - the symbol of the Katrina Dawson Foundation.
"Let's just make it a really happy day, and hopefully the staff have a great day and by the end of it we're all in a really good place," he said.
- Daily Mail