Dummett began his career with his local side Newcastle United. After progressing through the youth ranks at the club, he had loan spells at Gateshead and Scottish side St Mirren. He made his Premier League debut in the 2013–14 season and scored his first Premier League goal against Liverpool on 19 October 2013. Dummett is a first team regular for Newcastle United and was part of their promotion from the Championship. Dummett is also Vice-Captain of the club.
Dummett started his career in the Newcastle United youth system, captaining the club's reserve team on several occasions.
Dummett joined Conference National side Gateshead in March 2012, initially for a month-long loan, which was then extended until the end of the season, helping the team keep six clean sheets from ten matches.
The following season he was loaned to Scottish Premier League club St Mirren. Dummett made his debut in a 2–0 win over Hearts on 15 September 2012, and scored his first senior goal in a 1–1 draw against St Johnstone.
After returning from his loan spell at St Mirren, Dummett made his debut senior appearance for Newcastle in an FA Cup tie away defeat to Brighton & Hove Albion on 5 January 2013. After the match, Dummett spoke out on his debut, that his Newcastle United debut was a dream come true. He then rejoined St Mirren on 31 January 2013 on loan for the rest of the season. Dummett played the full game for St Mirren in their Scottish League Cup Final 3–2 win over Hearts, the club's first major cup for 26 years. Dummett also set up the second St Mirren goal in the 46th minute, for Steven Thompson, which put the Saints 2–1 up.
Dummett returned to Newcastle, and signed a one-year contract extension. He made his debut for the club as a substitute during a 4-0 defeat to Manchester City on the opening fixture of the 2013-14 season, coming on after a sending off of fellow defender Steven Taylor and playing the full second half of the game. He scored his first goal for Newcastle in a 2–2 draw at home to Liverpool in October 2013. Just weeks after scoring his goal for the club, Dummett put pen-to-paper on a new contract at Newcastle, signing a deal that could extend until 2019.
On the final day of the season, Dummett made a challenge on Liverpool forward Luis Suárez. Due to knee surgery which jeopardised Suárez's chances of playing at the 2014 FIFA World Cup, fans in his native Uruguay sent online death threats to Dummett.
Dummett started the 2014–15 season as Newcastle's first-choice left-back, with Davide Santon injured and Massadio Haïdara on the bench. Dummett grabbed his second Magpies goal on 25 September 2014, scoring a late winner in extra-time against Crystal Palace in the League Cup. Playing alongside captain Fabricio Coloccini in the centre of defence, Dummett helped Newcastle keep clean sheets in victories over Manchester City and West Bromwich Albion. On 12 January 2016, Dummett scored a 90th minute equalizer against Manchester United in a match that ended in a 3–3 draw at St James' Park.
Dummett qualifies to play for Wales through his Welsh grandfather. He was capped at under-21 level for Wales. He made his senior debut for Wales in the match against the Netherlands on 4 June 2014, coming in as a substitute in the 83rd minute. Dummett played his second international match on 13 November 2015, again against the Netherlands, coming on for Neil Taylor in 65th minute. In May 2016, Dummett was listed for the 29-man squad for a pre-Euro 2016 training camp. However, Dummett was among six players to be cut for the Euro 2016 squad. In May 2017, Wales manager Chris Coleman said that Dummett would no longer make himself available for international selection.As of 16 August 2017
As of 8 January 2016.
Newcastle United FC
EFL Championship: 2016–17
Scottish League Cup: 2012–13