Central Otago Mayor and Mayoress Tony and Bernie Lepper cut the ribbon after speeches in front of about 200 people on Saturday morning.
Mrs Lepper, also the house trust chairwoman, said it was a ''really great feeling'' to be there after so much hard work for ''a building that has changed the landscape of Central Otago''.
Mr Lepper said the project had not been without difficulties but they had been overcome.
''Hurdles have been encountered, worked through and beaten.
''None of this has happened by luck ... [but by] the vision of dedicated and intelligent people.''
After the speeches, the planting of a commemorative tree and a blessing by Reverend Martin Oh, people had the chance to walk through the building.
''It's absolutely magnificent, a great effort and a whole new look for Alexandra,'' Margaret Popenhagen, of Alexandra, said.
Her comments were echoed by many as they walked the hallways, looked in offices or had a cup of tea in the reception area.
Another common remark was the amount of space and attention to detail for the price tag.
Waitaki MP Jacqui Dean was one of those having a look.
''What strikes me first of all is that it's such a well-thought-out building ... combining and bringing together all of what this community needs.''
The 1054sq building, in the St Enoch's Church grounds in the centre of Alexandra, now houses social service agencies, along with education and arts and crafts groups such as Central Otago Rural Education Activities Programme (Reap), the Alexandra Community Advice Network, the Central Otago Budgeting Service, Plunket, Relationship Services, Catholic Social Services, Anglican Family Care, Alzheimer's Society, Age Concern, Central Otago District Arts Trust, Jigsaw, Cancer Society and the Youth Clinic.
The $2.6 million cost had been raised by community groups and individuals, with major grants coming from the Central Lakes Trust, Lotteries Community Fund, Transpower, the Otago Community Trust, the Alexander McMillan Trust, Pub Charities and the Vincent Community Board.
Three buildings were removed or demolished to make way for the complex:
the church house and hall and a building known as Ranby House.
An oak tree was also removed and has since been made into an outdoor seat at the house by the Alexandra Men's Shed group.
