[4][5] His professional career began in the British Darts Organisation (BDO) events but he only competed in one major tournament, the 2003 Winmau World Masters, losing in the last 128.

[7] He failed to qualify for the 2005 World Championship, but back at Bolton for the 2005 UK Open he produced one of the rare whitewashes in the tournament's history, beating Colin Monk 11–0 before falling 11–8 to Chris Mason in the last 16.

[9] In late 2005, Lewis began to produce some promising results, including reaching his first major event quarter-final in the 2005 World Matchplay, where he lost to Colin Lloyd.

[7][10] Lewis made his PDC World Championship debut in 2006, reaching the quarter-finals by defeating Dave Honey, Dennis Priestley and Roland Scholten.

[13] His ranking continued to rise by reaching the latter stages of the non-televised PDC Pro Tour events during 2006 (including winning a Scottish Players Championship) as well as the last 16 of the UK Open, having beaten Wayne Mardle 11–10 in the last 32, before losing to John MaGowan 11–6.

[26] He won his first PDC Pro Tour event in three years at the Austrian Players Championship, where he beat Carlos Rodriguez 6–4 in the final, which included a nine dart finish.

He added another Pro Tour title the following month at the Irish Open Players Championship beating Andy Hamilton in the final by 6 legs to 4.

[28] Lewis proceeded to make it to the final of the 2011 Premier League but lost 10–4 to Gary Anderson after beating Phil Taylor 8–3 in the semi-final in the same night.

[33] More comfortable victories ensued over Robert Thornton (4–2) and Wayne Jones (4–0), with Lewis seemingly heading for the semi-finals as he led Terry Jenkins 3–0 in the last 8, having only lost 2 legs.

[32] The tournament victory took Lewis' career prize money above the £1 million mark,[10] and confirmed his number two status in the PDC Order of Merit.

[39] Lewis maintained his form for his next tournament of the season as he represented England and won the 2012 PDC World Cup of Darts, with Phil Taylor.

The pair needed a sudden-death leg to see off Canada in the second round, before defeating the United States and Wales to reach the final where they played the Australian team consisting of Simon Whitlock and Paul Nicholson.

[46] Lewis lost in the last 32 of the UK Open 7–9 to Wes Newton,[47] and in the final of the seventh Players Tour Championship of the season, 3–6 to Ronnie Baxter.

[49] In September, Lewis won his first individual title since his World Championship win at the fourth European Tour event, the German Darts Masters in Stuttgart.

He dropped just three legs in his first three games before beating Tony West 6–3 in the quarter-finals and James Wade 6–1 in the semis to face occasional practice partner Ian White in the final.

[51] After losing his opening two games of the Grand Slam of Darts to Tony O'Shea and John Part, Lewis failed to qualify from his group for the fourth time in the six stagings of the tournament.

They survived two match darts from South Africa in the last 16 and one from Wales in the semi-finals to play the Belgian brothers Ronny and Kim Huybrechts in the final.

[67] Lewis beat Ronny Huybrechts, Brendan Dolan and Andy Hamilton at the World Matchplay to once again face van Gerwen in the semi-finals of a major event.

[70] In October, Lewis won his first Pro Tour title in over a year at the ninth Players Championship as he came from 3–0 down in the final to beat Brendan Dolan 6–4.

[71] Lewis almost pulled out of the inaugural Masters tournament due to a bout of flu before edging past Kim Huybrechts in the first round 6–5 and then thrashing home favourite Robert Thornton 8–2.

[80] More comfortable wins over Raymond van Barneveld (9–2) and Mensur Suljović (10–3) followed before Lewis beat Mervyn King 10–6 to play Terry Jenkins in the final.

[88] Lewis threw a nine-dart finish to win the opening set of his third round tie against Raymond van Barneveld at the 2015 World Championship.

[100] He suffered a surprise 13–10 loss to Gerwyn Price in the second round of the World Matchplay and was thrashed 11–3 by Taylor in the final of the Sydney Darts Masters.

[106] A trio of matches without dropping a set saw Lewis cruise in to the quarter-finals of the 2016 World Championship and he then overcame Peter Wright 5–2 and was 5–0 up on Raymond van Barneveld in the semis.

[110][111] Lewis ended Michael van Gerwen's 27 match wins in a row when he knocked out him 6–4 in the quarter-finals of the first Players Championship event of the year.

[112] Lewis advanced to the Premier League Play-offs for the first time in five years, which included a nine darter against James Wade in week 11, but he was easily defeated 10–4 by Van Gerwen.

[115] Anderson inflicted an 11–7 defeat on Lewis in the final of the Auckland Darts Masters and he lost 17–9 to Van Gerwen in semi-finals of the World Matchplay.

[120] He was beaten 6–4 by Peter Wright in the final of the first UK Open Qualifier of the year and won the fifth Players Championship with a 6–3 victory over Dave Chisnall.

On 2 February 2018 the Darts Regulation Authority ("DRA") released a statement that Lewis would be suspended with immediate effect pending an appeal following an incident with José Justicia in the first UK Open qualifier.

[citation needed] On 6 August 2012, he married Sarah Podmore (born 1987), who has three children from her previous marriage, and in December 2012 gave birth to their son Matthew.