The new store, which is on the site of the former Homebase on Winchester Road, is 84,500sq ft and offers customers more than 30,000 home improvement and garden products.
Services include paint mixing, key cutting, a garden centre, Indoor play area, café, timber cutting and in-store DIY workshops.
To celebrate the opening, British Olympic gold medallist James Cracknell joined a welcome breakfast staff.
The store hosted two days of events last weekend (December 16-17) with family activities including the famous Bunnings Sausage Sizzle, face-painting, balloon modelling and a story time session led by Santa.
Bunnings, which is a leading retailer of home improvement and outdoor living in Australia and New Zealand, acquired Homebase for £340 million in February 2016 – and plans to invest a further £500 million building the Bunnings Warehouse business in the UK and Ireland over a five-year plus timeframe.