The newly installed leader will speak with her counterparts from New Zealand and Australia on Saturday, with the conversations framed by No.10 as chats rather than formal bilateral meetings.
Downing Street suggested they would be an opportunity for condolences over the Queen's death, with politics likely to come up.
The first of the weekend's meetings will be based at the government's Chevening country residence, rather than the PM's official country residence Chequers, which is said to be undergoing routine maintenance work after the departure of former leader Boris Johnson.
Ms Truss will see Australia's Prime Minister Anthony Albanese, and New Zealand's leader Jacinda Ardern on Saturday.
Ms Ardern has said the Queen's death and new King will be the "focus of conversation", with the pair also likely to discuss Ukraine and the UK's free trade agreement with New Zealand.
But all will be "within the context of the week of mourning that the UK is currently in".
The conversation between Ms Truss and Mr Albanese may also touch on trade, with the countries last year signing a deal estimated by the government to be worth Stg 2.3 billion ($A3.9 billion) to the UK economy.
Ms Truss also has a packed diary on Sunday, with plans to meet US President Joe Biden, Irish Taoiseach Micheal Martin, Canadian premier Justin Trudeau and Polish leader Andrzej Duda at Downing Street.
Ms Truss previously met Mr Biden as foreign secretary, but this will be their first in-person conversation since she became prime minister.
It will take place against a backdrop of disputes over the Northern Ireland Protocol triggered by Britain's leaving of the European Union, and difficulties working towards a trade deal with the White House.
The controversial post-Brexit treaty is also likely to come up when she speaks to Mr Martin, amid strained relations between the two countries over the trading arrangements.
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