Mr Garratt said Sir Michael's pledge led the way for "a month of giving". Project backers were encouraging people to dig deep this month, with one year to go until the June 2017 funding deadline, stipulated in last year's binding referendum.
Sir Michael's company's pledge helps bring the HAC closer to the $16.25m needed to complete the building. The HAC project now has $10.3m in donations.
"It is wonderful to have the likes of such well-respected New Zealanders on board with us," Mr Garratt said.
Mr Hill's support of art and culture dates back to childhood, Mr Garratt said. The entrepreneur began as a musician and watch-maker before directing his creativity into jewellery.
Michael Hill Jeweller now has 314 stores in New Zealand, Australia, Canada and the US, and aims to operate 1000 stores by 2022.