Pentwyn is an electoral ward in the northeast of Cardiff, capital city of Wales.

[2] Councillor Judith Woodman, who won her Pentwyn seat at a 2003 by-election and had been deputy leader of the council and leader of the Liberal Democrat group, stood down at the May 2017 election.

[7] Labour council leader Russell Goodway was increasingly unpopular and his administration was facing a challenge from the Liberal Democrats.

[7] The Labour Party also faced a challenge from the left, with the Welsh Socialist Alliance fielding the secretary of the South Wales Fire Brigades Union as a candidate.

[7] The resulting "disastrous showing" for Labour and the "landslide" victory for the Liberal Democrats led to a local vote of 'no confidence' in Cllr Goodway, with a further vote of no confidence discussed by the county Labour Party in October.