Porter joined Leyton Orient on a two-week trial in May 2010, playing in several reserve games, and he was signed by the O's in May 2010. He made his first appearance in an Orient shirt in a friendly match against his old club on 14 July 2010, winning a penalty in a 2–0 win. His league debut came in the 3–1 defeat at home to Charlton Athletic on 13 August, when he appeared as a substitute. On 29 October 2010, after a period of illness, Porter signed on a month's loan to Conference South club Lewes. He made his debut for the Rooks on 30 October, in the 1–1 draw with Dartford. In his next game, a 3–0 win at Weston-super-Mare, Porter scored his first goal for Lewes, but was later sent off. Porter's Lewes loan was extended, but at the end of January 2011, he went on loan to Hastings United, where he made his debut in the 2–2 draw at home to Folkestone Invicta on 1 February. He scored his first goal for Hastings in the 3–2 victory over Tooting & Mitcham United on 12 February. At the end of the season, Porter returned to Orient and scored a hat-trick for the O's in a 5–0 demolition of Finnish second division side SJK during their pre-season tour of Finland. He made his first start for Orient and scored his first professional goal on 17 September 2011, in the 3–1 defeat at home to Oldham Athletic. A string of impressive performances, including a goal in his FA Cup début against Bromley, soon saw him attract interest from the likes of Nottingham Forest and Ipswich Town. On 23 May 2012 Porter rejected a two-year contract offer from Leyton Orient leaving the club to expect his departure.
On 3 July 2012, Porter signed for Football League Championship club Burnley on a three-year contract. Porter picked up an injury before the start of the season.
He signed on a youth loan for Colchester United on 1 January 2013 until the end of the season and made his début the same day, coming on after 73 minutes as a sub in the 3–0 defeat at Crawley.
On 18 July 2013, it was announced that Porter had joined League Two side AFC Wimbledon on a season-long loan deal. AFC Wimbledon manager Neal Ardley said of Porter joining "The Dons" that "the pacy forward is likely to be utilised on the flank" and "George is very quick and direct; he will give us real high energy and creativity in the final third", with Porter himself stating that he "cannot wait to get started at AFC Wimbledon having been impressed by the club's support in the past". Porter made his first appearance for "The Dons" two days later in a pre-season friendly game against Conference South sideSutton United at Gander Green Lane that resulted in a 4–0 win. However, he was substituted after only six minutes due to an injury, though this did look more precautionary than anything serious. On 24 January 2014, Porter returned to Burnley early from his loan after falling out of favour at Wimbledon, amid rumours of a training ground bust up with manager Neal Ardley. He made a total of 24 appearances scoring no goals.
2014–15
On 31 January 2014, Porter signed for Rochdale on a short-term deal until the end of the season, following his departure from Burnley. He subsequently joined League Two club Dagenham & Redbridge before returning to the Isthmian LeaguePremier Division and joining leaders Maidstone United.
In July 2015, he signed for National League side Welling United on a free transfer.
Bromley
In June 2016, Porter signed for fellow National League side Bromley following his departure from relegated Welling United. Despite missing a considerable period through injury, Porter made 31 league appearances, scoring 6 goals, and was rewarded with a new one-year contract at the end of the season.
