I would like to do my father's haj as he passed on 3 years ago from severe illness. Prior to this, I promised him that I will do his haj if he does not get an opportunity to do it. My husband will be my mahram. Is it fine for a daughter to do her father's haj?

It appears that your doubt stems from the principle of whether a male can perform Hajj-e-Badal on behalf of a female and vice versa. The issue is not confined to the situation between a daughter and father.

In principle, it is permissible for a male and female to perform Hajj-e-Badal on behalf of one another. The male and female do not have to be Mahrams to each other.

and Allah Ta'ala Knows Best

Mufti Ebrahim Desai