The government has scrapped plans to reduce the number of parliamentary constituencies from 650 to 600.
Proposals that would have seen the Montgomeryshire constituency disappear, and the size of Brecon and Radnorshire extending will not go ahead.
Cabinet office minister Chloe Smith revealed that ministers will abandon the coalition-era plans because parliament will have a "greater workload" following Brexit.
Former Montgomeryshire MP Glyn Davies, who strongly opposed the plans, said it was an "utterly daft proposal" that would have "destroyed parliamentary democracy in Mid Wales".
The proposals would have seen north Montgomeryshire, including Welshpool, merged with South Clwyd; most of south Montgomeryshire, including Newtown, with Brecon and Radnorshire; and Machynlleth merged with Ceredigion and North Pembrokeshire.
Despite plans to make the House of Commons smaller being dropped, Wales is still set to lose around eight MPs because ministers still want to create constituencies with a near-equal number of voters.
Mr Davies said: "It’s good in that 650 seats might allow for a Mid Wales constituency, hopefully taking in most of Montgomeryshire that we can recognise as serving much the same area - though with a somewhat larger population."
Boundary reviews will now take place every eight years, instead of five, to allow updated constituencies to be in place for two general elections.
The Boundary Commission will be asked to draw up a new map of constituencies in a review that is due to begin in early 2021.
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