Webb represented Wales at under-16, under-18, under-19 and under-20 levels, as well as in international rugby sevens, before making his debut for the senior national team in 2012.

Webb is currently serving a four year ban due to end in June 2027 in relation to an anti-doping rule violation after testing positive for human growth hormone (HGH) in July 2023.

He made his debut for the senior regional side in March 2008, coming on as a substitute for Shane Williams in a 32–7 win over Ulster.

[4] He made another substitute appearance in a 19–18 loss to Edinburgh a month later, replacing Justin Marshall,[5] before starting the final two games of the season against the Newport Gwent Dragons and Connacht.

[13] An ankle injury suffered in Wales' opening Autumn international against Australia on 5 November ruled him out for up to 12 weeks, but recovered slightly ahead of schedule,[14] and scored within four minutes of his return to club rugby as he captained the Ospreys to a 26–21 win over Newcastle Falcons in the Challenge Cup on 21 January.

[16] On 10 October 2017, it was announced that Webb would leave Ospreys after 10 years with the region to join French club Toulon in the Top 14 on a three-year contract.

In March 2018, Webb suffered a knee injury and missed the remainder of the season, bringing his time with the Ospreys to a premature end.

Recalled during the 2016 Six Nations Championship after a remarkable recovery, producing man-of-the-match performances for the Ospreys, Webb replaced Davies at scrum-half during the match against England.

Webb began the 2016 Autumn internationals as Wales' first-choice scrum-half, but suffered a serious ankle injury during the second half of their opening match against Australia, and following surgery was ruled out for 12 weeks, with his return predicted for just prior to the 2017 Six Nations Championship.

[43] Webb found himself out of Wales reckoning under Wayne Pivac, but was recalled by returning head coach Warren Gatland for the 2023 Six Nations squad.