1918–1983: The Urban Districts of Bridgend, Maesteg, and Ogmore and Garw, and part of the Rural District of Penybont. 1983–2010: The Borough of Ogwr wards of Bettws, Blackmill, Blaengarw, Caerau, Llangeinor, Llangynwyd, Maesteg East, Maesteg West, Nantyffyllon, Nant-y-moel, Ogmore Vale, Pencoed, Pontycymmer, St Bride's Minor, and Ynysawdre, and the Borough of Taff-Ely wards of Brynna, Gilfach Goch, Llanharan, and Llanharry. 2010–present: The Bridgend County Borough electoral divisions of Aberkenfig, Bettws, Blackmill, Blaengarw, Bryncethin, Bryncoch, Caerau, Cefn Cribwr, Felindre, Hendre, Llangeinor, Llangynwyd, Maesteg East, Maesteg West, Nant-y-moel, Ogmore Vale, Penprysg, Pontycymmer, Sarn, and Ynysawdre, and those in Rhondda Cynon TaffCounty Borough of Brynna, Gilfach Goch, Llanharan, and Llanharry. Taking its name from the River Ogmore, the constituency is close to the source of the river in the Ogwr valley, but it excludes the village of Ogmore-by-Sea, south-west of Bridgend. Ogmore constituency covers the area of Bridgend County Borough Council roughly north of the M4, and parts of Rhondda Cynon Taf County Borough Council. It includes the communities of Cefn Cribwr, Garw Valley, Gilfach Goch, Llanharan, Maesteg, Ogwr Valley, Pencoed, Sarn and Tondu. ;Major boundary change A substantial change of boundaries took effect in 1983, when the new constituency of Bridgend was set up, centred on the town of that name, which was by then the largest settlement in Ogmore.
History
;Summary of winning results The 2015 result made the seat the 44th-safest of Labour's 232 seats by percentage of majority. Successive candidates fielded by the Labour Party have won absolute majorities since the seat was created in 1918, or have run unopposed four times. The 2019 election was the first time in the seat's 101-year history that Labour failed to win an absolute majority, though the party still won with a margin of 22% ;Opposition parties Four parties have taken the runner-up position from and including a 2002 by-election, a total of five elections. At the 2015 general election the Liberal Democrat, Green and TUSC candidates did not win 5% of the vote apiece therefore forfeited their deposits. Those running for the Conservatives and UKIP in 2015 held their deposits. The highest polling of any runner-up, by percentage, was Thomas George Jones in 1931, winning 30.8% of the votes cast, 0.3% more than the half-total of the winning candidate and in an election when the pre-World War II Labour Party's vote was slightly split by the presence of a prominent Communist Party candidate and editor, Johnny Campbell, the government's ceasing of prosecution of whom in 1924 led to a General Election. ;Turnout Turnout at general elections has ranged between 85.3% in 1950 and 57.8% in 2005, falling to 35.2% in the 2002 by-election.
