Montgomeryshire (Welsh: Sir Drefaldwyn) was a constituency[n 1] in Wales represented in the House of Commons of the UK Parliament.

It was abolished following the 2023 Periodic Review of Westminster constituencies prior to the 2024 general election and replaced by Montgomeryshire and Glyndŵr.

The seat was based on the ancient county of Montgomeryshire, in the principal area of Powys.

At the time of its abolition, Montgomeryshire was the only seat in Wales never to have elected a Labour MP.

Under proposed constituency boundary changes announced in September 2016, ahead of the next general election, the seat was to be partitioned, the northern half including Welshpool to be merged with Clwyd South to form a new seat of South Clwyd and North Montgomeryshire; most of the southern including Newtown was to be merged with the Brecon and Radnor seat to form a seat renamed as Brecon, Radnor and Montgomery,[3] and the wards of Llanidloes and Blaen Hafren merged into the Ceredigion constituency which would form part of a new seat called Ceredigion and North Pembrokeshire.