Ynys Môn is also one of nine constituencies in the North Wales electoral region, which elects four additional members, in addition to nine constituency members, to produce a degree of proportional representation for the region as a whole.

It was represented from 1999 by Ieuan Wyn Jones, the former leader of Plaid Cymru.

Jones resigned from the Assembly on 20 June 2013, triggering a by-election, which was held on 1 August 2013.

[1] Plaid Cymru's candidate Rhun ap Iorwerth comfortably held the seat for the party with a majority of over 9000 votes.

As created in 1999, the North Wales region includes the constituencies of Alyn and Deeside, Caernarfon, Clwyd West, Clwyd South, Conwy, Delyn, Vale of Clwyd, Wrexham and Ynys Môn.