"The acquisition of Westfield is a natural extension of Unibail-Rodamco's strategy of concentration, differentiation and innovation", Unibail chief executive Christophe Cuvillier said. The company also is developing malls in Brussels and in Hamburg, Germany.
Unibail-Rodamco invests in commercial property, from malls to office space, mainly in mainland Europe.
The transaction would create a global operator and developer of flagship shopping centers spanning the USA and Europe, with a gross market value of US$72.2 billion.
An emotional Lowy said he and his sons will continue to serve in advisory roles to the new company, while his family will maintain a "substantial investment in the group".More news: Carson Wentz has torn ACL, done for season
The combined company, which will use the Westfield name, will own 104 assets attracting 1.2 billion visits annually, "creating a must-have partner for all global retailers and brands across Europe and select markets in the United States", the companies said in a joint statement.
Westfield started in 1959 with one shopping center in a suburb of Sydney, Australia, and was first listed on the Australian Stock Exchange the following year, according to its website.
Not yet. Unibail-Rodamco's value fell as much as 4.1% on news of the deal.
A 90% interest in OneMarket, Westfield's retail technology platform, will be spun-off into a newly formed entity.More news: Trump slams 'fake news media', wants some reporters to be fired
"Unibail is mounting the biggest takeover of a company in the Asia-Pacific region this year - and the largest ever in Australia - as mall owners seek to contend with relentless pressure from online commerce".
Frank Lowy, Westfield's chairman, said "the transaction announced today is the culmination of the strategic journey Westfield has been on since its 2014 restructure".
Unibail said it had identified cost savings of £88million, including £53million from slashing corporate overheads.
Westfield's portfolio includes shopping areas at USA airports such as Newark Liberty International, John F. Kennedy International, Los Angeles International and Orlando International.More news: Met Office issues amber warning for Derbyshire — SNOW ALERT
Oh, and last Friday he was knighted by Queen Elizabeth "for his contribution to the British economy and philanthropic efforts in the country".