An election to the 57th Parliament of the United Kingdom for the constituency area of Cynon Valley, held as part of the general election on 8 June 2017.
Labour hold by Ann Clwyd with a majority of 13,238 - 41.6% - on a turnout of 62.0%.
Candidates
| Name | Party | Vote | Vote share | Vote change |
| CLWYD, Ann | Lab | 19,404 | 61.0% | 13.3% |
| DEWHURST, Keith | Con | 6,166 | 19.4% | 7.3% |
| WALTERS, Liz | PC | 4,376 | 13.8% | -3.1% |
| MCLEAN, Ian | UKIP | 1,271 | 4.0% | -12.3% |
| KNIGHT, Nicola | LD | 585 | 1.8% | -0.9% |
Under section 13(b) of the Representation of the People Act 1985, a candidate gaining 5% or less of the vote share will forfeit their deposit.
An electorate of 51,334, having a valid vote count of 31,802 and an invalid vote count of 71.
Result declared at 02:27 on 9 June 2017.