The new firm, branded Mossgreen, will initially incorporate the Leski name for collector's categories.
We reported in ATG No 2083 how Bonhams had launched a new office and saleroom in Melbourne, with the first auction - Australian and Aboriginal art - coming up on May 15.
At Mossgreen, a new board will comprise Jack Gringlas as non-executive chairman, Charles Leski as managing director of Mossgreen Collectors Auctions and Paul Sumner as managing director of single-owner and Asian art auctions and Mossgreen Gallery.
The new firm will relocate to the historic Armadale Picture Theatre building in Melbourne. The former home of Sotheby's will be refurbished by September and will also house the Mossgreen Gallery.
Mr Leski said: "The merger will present us with opportunities to achieve even greater market penetration, which will instil confidence in buyers and sellers globally."
Mr Sumner, who established Mossgreen in 2004 as a single-owner auction specialist and gallery, was previously managing director of Sotheby's in Australia and chairman of Sotheby's Olympia.
Mr Gringlas is the former owner and managing director of CMG Engineering Group, which operated in eight countries, specialising in electric motors and related products. In 2010, he sold CMG to Regal Beloit Corporation of the USA, giving him the financial clout to invest in this new firm.