Washington H Soul Pattinson and Company and Brickworks will join forces in September, undoing a unique 56-year cross-ownership structure in which each owned shares in the other.
"This is a monumental day in the history of our company, Soul Pattinson, and for Brickworks as well," chairman Robert Millner told shareholders, more than 95 per cent of whom voted to approve the deal.
Soul Patts was founded in 1903 as an Australian pharmacy operator but today operates as an investment house with a diversified portfolio of unrelated assets.
Technically, both companies are being acquired by a new company, TopCo, but once the deal is complete it will be renamed Washington H Soul Pattinson and Company and use its SOL ticker code.
Brickworks will be moved from the ASX200 and will be replaced by Catalyst Metals, a WA gold producer.
Soul Patts lead independent director David Baxby said the merger would simplify the corporate structure and create a stronger, more diversified investment house.
"I think we'd all recognise that there's a certain level of bureaucracy and distraction associated with being a public company, so bringing both groups together and removing one layer of that is obviously an opportunity for just greater focus on the underlying business," he said.
There might be some level of cost savings that could be achieved by the merger, but that wasn't an active driver of the deal, Mr Baxby said.
As part of the deal, Topco is raising another $1.4 billion, funds that will be used to pay down Brickworks' debt and strengthen the new company's balance sheet.