The official opening also had ties with the original laying of the foundation stone on September 18, 1890.
The ribbon to the extension from the main hall was cut by the great-grand-daughter of Robert Jackson, who laid that foundation stone.
She was invited from Christchurch for the occasion and told about 220 people she was "absolutely thrilled" to be there and be included in "such an auspicious occasion".
The extension follows about nine years of planning by the Weston Progress League and incorporates upgrading of the existing hall, building a new extension including a commercial kitchen, supper-meeting room and modern toilet facilities, plus an entrance and foyer from the car park.
The upgrade was needed to meet the modern demands of a growing community, including the Weston School across the road, which uses the hall for wide-ranging activities.
League chairman Derek McGee paid tribute to all those involved in the project, from organisations who made grants, through to the contractor and subcontractor who completed the almost year-long project.
He said the community was not only looking after the assets it had, but also leaving them enhanced for the following generations.
Weston School principal Nicky Ryan said she believed the hall would be a treasure and noted the first celebration in the hall would be on Friday when the school was to hold its assembly.
Two children from Weston School, year 8 pupil Brooklyn Johnston and year 7 pupil Whitney Cleveland, gave their recollections and a history of the hall, then looked ahead to its use in the future.
The extended hall was then blessed by the Rev Nancy Parker, followed by the cutting of the ribbon and a tour, led by highland pipers Nicholas Parsons and Lachie Brown, through the extension.
