Bristol Sport Ltd, which owns the football club, wants to replace two stands to increase capacity.
The plan is an alternative to proposals to build a new stadium at nearby Ashton Vale, which has been delayed by an application for a town green.
Majority shareholder Steve Lansdown confirmed the club would begin work at a shareholder meeting on Tuesday.
The work was approved by Bristol City Council in November.
Mr Lansdown told the club's official website: "We'll sign the section 106 agreement any day now, and then we have six weeks to wait for the judicial review period.
"We wanted to give some certainty to supporters, so if we get through to March with no judicial review, then we will be going ahead with the redevelopment plans, starting in May."
A £40m revamp of Bristol City's Ashton Gate ground will go ahead this summer, the club has announced.