英國 "以最有力的方式 "開始了談判，但尤斯提斯先生說，特拉斯女士要求在2021年6月11日康沃爾七國集團會議前就協議條款達成一致，這讓談判人員 "陷入了困境"。
他說，英國需要從這些 "失敗 "中吸取教訓，並將農業和食品談判的責任轉移到Defra。
Mr Eustice, who helped secure the agreement, told a Commons debate that it was "not actually a very good deal for the UK".
At the time the government estimated the Australia-UK Free Trade Agreement, signed on 17 December 2021, would unlock £10.4bn of additional trade while ending tariffs on all UK exports.
The deal also removed some visa rules. Young people are now able to work and travel in Australia for up to three years. UK architects, scientists, researchers, lawyers and accountants can also access work visas without being subject to Australia's skilled occupation list.
Mr Eustice told the Commons that now he is on the backbenches he "no longer has to put such a positive gloss on what was agreed".
Overall the UK "gave away far too much for far too little in return", he told MPs.
This includes giving Australia or New Zealand full access to the UK market to sell beef and sheep, while Australia still bans the import of British beef, he added.
Mr Eustice worked in the Department of Environment, Food and Rural Affairs (Defra) for nearly a decade - first as a minister before being appointed secretary of state by Boris Johnson.
The UK started negotiations "with the strongest possible hand" but Mr Eustice said negotiators were put "on the back foot" by Ms Truss demanding that the terms of the deal were agreed before a meeting of the G7 in Cornwall on 11 June 2021.
He said the UK needed to learn from these "failures" and move responsibility for negotiations on agriculture and food to Defra.