Perry Tian-Hee

On 1 November 2014, he had his first inclusion in a matchday squad, remaining an unused substitute in a 1–1 draw at Crawley Town in League One.

On 30 January 2015, Ng was loaned for a month to Hyde United of the Conference North. He made his senior debut on 7 February, playing the full 90 minutes of a 1–3 home loss to Boston United. Ng twice extended his loan for the struggling team, eventually for the remainder of the season. He totalled 13 appearances, all starts, as they ended the season bottom of the table, and scored his first senior goal on 14 March, a last-minute equaliser in a 1–1 draw with Harrogate Town at Ewen Fields.

On 27 November 2015, Ng made his debut for Crewe, coming on in added time in place of Ryan Colclough in a 1–0 win over Oldham Athletic at Gresty Road. He made Crewe's starting XI for the first time on 5 May 2016 against Burton Albion at Gresty Road.

On 22 May 2017, Ng signed a new one-year deal, including an option for a further 12 months depending on appearances. He was sent off for two bookings in 17 minutes on 12 August in a 1–1 home draw with Newport County. Four weeks later, on 9 September 2017, he scored his first Crewe goal in a 5–1 win over Chesterfield at Gresty Road.

On 3 January 2018, Ng was retrospectively suspended for four games following an off-the-ball clash with Cambridge United's Jabo Ibehre in a match at the Abbey Stadium on 30 December 2017. Ng's left-footed strike at Stevenage on 10 March 2018 was named the League Two Goal of the Month winner for March.

Ng was Crewe's Player of the Year and Players' Player of the Year for 2018–19, with manager David Artell praising his consistency despite not scoring a goal all season. The following season (2019-20), Ng helped Crewe to automatic promotion to EFL League One in a campaign shortened due to the COVID-19 pandemic, with Ng widely selected by regional football journalists in their "League Two team of the season (so far)". In September 2020, Ng (along with Crewe team-mate Charlie Kirk) was named in the PFA League Two Team of the Year for the 2019-20 season.

Ng was suspended for six matches following a breach of FA Rule E1 (spitting) after an FA Cup tie at Cheltenham Town on 28 November 2020.

Cardiff City
In early January 2021, Artell rejected an initial offer for Ng, reportedly £250,000, from Championship side Cardiff City. On 19 January 2021, Ng's transfer to Cardiff, for an undisclosed fee, was confirmed; the BBC reported Cardiff would pay Crewe an initial £350,000, which could rise to £500,000. He made his debut on 20 January 2020 in Cardiff's 1–0 home defeat against Queens Park Rangers.

International career
Ng is eligible for the Singapore national football team through his paternal grandfather. He told FourFourTwo in May 2017 that he wanted to represent them and had been contacted by the Football Association of Singapore.