The official opening was on Saturday, although the campus had been operating for a week.
Mr Cull said the Oxford St buildings looked "pretty sad" for a time after the school closed last year.
Now, early learning centre Little Citizens and a family services hub occupy the former school. Previously, the family facilities were in smaller premises on Wesley St.
Mr Cull said the facility was an asset for South Dunedin, providing a focal point not just for young families, but the wider community.
He commended the Methodists for investing in the new facility at a time when money for social development projects was tight.
Also speaking at the opening ceremony, the mission's chief executive Laura Black thanked Mercy Hospital's charitable trust for a grant for the centre.
She joked Catholics and Methodists did not usually get on well together, alluding to Mercy's tie with the Sisters of Mercy.
Mercy Hospital chief executive Richard Whitney said the centre was accessible, friendly, and well-targeted.
"If that is not a recipe for success, I'm not sure what is," Mr Whitney said.
Mercy Hospital, which had historic ties with social outreach in South Dunedin, was proud to be part of the venture, he said.
