Qatari investment funds are understood to have agreed to pay about £30million cash for Mr Halabi's stake in the site over London Bridge station, where there are plans for a 310m (1,016ft) skyscraper and adjoining low-rise glass edifice that could in total be worth £1.4 billion if built and fully let.
The final terms of Mr Halabi's sale are expected to be similar to those of a deal struck last week between the same Qatari funds to buy another one-third stake in the Shard scheme from CLS Holdings, a quoted property company that was forced to book a £25 million loss on its investment.
CLS's last gross value for its one-third stake in the Shard was £131 million, based on a June market estimation.
However, Mr Halabi, a reclusive Syrian-born private investor, is likely to have kept his investment in the scheme at cost.
His family trust is thought to have invested about £10.5 million to buy his one-third stake in the scheme, but it would have been liable for finance costs and advisory fees to keep the project alive.
Mr Halabi is sitting on losses of up to £150 million after buying the Esporta fitness chain last year, only for Société Générale, his main bank lender for the purchase, to put the holding company into administration. The Qatari funds buying into the Shard are thought to be fronted by QInvest, a Doha-based Islamic bank that was formed last year with backing from Gulf Finance House.
The new Qatari owners are expected to draw up a deal with Sellar Property Group, the privately owned British developer, which will give each side equal control over the venture but leave Sellar in charge of the project development.
New ownership of the planned Shard and adjoining New London Bridge House may kick-start construction.