Langer was selected as an Australian rugby league schoolboy representative in 1982. At 15 Langer's first job out of school was a truckie's offsider, delivering whitegoods. He then worked for the council making roads, but continued playing football. Coached at the Ipswich Jets by former Australian international halfback Tommy Raudonikis, Langer became a key player for the club when he was only 17,
Coached by Bennett and captained under Wally Lewis at the Broncos, Langer developed further skill with the ball and learnt much from his mentors, and his two tries in Game I of the 1988 State of Origin series saw him named Man of the Match again. He scored tries in the other two Origin fixtures as well. On the 2nd Ashes Test of the 1988 Great Britain Lions tour which was played at Lang Park, on the electronic scoreboard the message "Bullfrog - shame our favourite No 7 isn't here" was displayed in a reference to Langer being overlooked for selection by Kangaroos team manager Peter Moore in favour of Peter Sterling. Langer made his debut for the Australian test side against Papua New Guinea due to a shoulder injury to Sterling. This made him the first Bronco to earn international representative honours. On 20 July 1988 Langer played for Australia in their record 62-point win over Papua New Guinea, scoring two tries. At the end of the 1988 NSWRL season Langer was named the Broncos' player of the year, then went on to score two tries in Australia's win in the 1988 World Cup final over New Zealand.
Suffering a broken leg in 1989, Langer missed a lot of football that season.
For Langer to play as he did, after a week of hearing how St George must stop him, confirms he deserves to be talked about with Peter Sterling and Wally Lewis as one of the three best players of the past decade.
Later in the year Langer also played in Australia's 1992 Rugby League World Cup final victory, and captained the Broncos to victory in the 1992 World Club Challenge, the first time Australian premiers had won the title on British soil. By this time Allan Langer's fame was such that he starred with his mother in the advertising campaign for Australia's top-selling bread and also had his own doll on toy store shelves.
The following season saw the Little General again lead the Broncos to a Premiership, the first time a team which had finished 5th in the regular season had gone on to win the competition.
In 1995, Alfie, along with many other high-profile players, lost their representative positions because they had signed contracts to play for the newly formed Super League. However Langer won the Broncos' player of the year award every year from 1993 to 1996. He was also made captain of the Queensland State of Origin team in 1996 and was named by Rugby League Week as that season's player of the year.
Langer again captained the Broncos to victory in the 1997 World Club Championship and the Super League premiership. In the first game of the 1998 State of Origin series Langer was named man-of-the-match. Also that year, for the second time, Langer captained the Broncos to a second consecutive premiership when they won the 1998 NRL grand final. In 1998, Langer was also appointed Australian national team captain. That year he and his mentor, Broncos, Queensland and Australian coach, Wayne Bennett, became the first captain-coach combination to win the NRL Premiership, State of Origin and Test series in the same year. Langer's 1998 season has since been described as one of the greatest individual seasons in Australian rugby league history.
Langer captained Warrington Wolves and took them to within one match of the Challenge Cup Final in 2000. Also in 2000, Langer was honoured as a Member of the Order of Australia "for service to Rugby League football as a player at national and international levels, and as a supporter of charities, particularly those raising funds for cancer research". Later that year he was also awarded the Australian Sports Medal.
As coach of the Maroons for the 2001 State of Origin series, Wayne Bennett made a surprise selection of Langer – then still playing in England – for the Queensland side in the third and deciding match. His comeback was arranged by Bennett under a shroud of secrecy. There were doubts as to whether Langer, in the twilight of his playing career, would be able to withstand the physical rigours of State of Origin football. Some Sydney journalists, such as Phil Gould, questioned the state of Queensland's football talent, given that they had needed to "bring back 35-year-olds to win." However on the night Langer set up two tries and scored one himself, leading Queensland to victory only a year after they had suffered their worst ever State of Origin defeat.
Langer was subsequently lured back to the Broncos for one final season in 2002. In doing so he became the NRL's oldest player that year at 36 years and 60 days. He was named man-of-the-match in the third and deciding game of that year's State of Origin series and became the oldest player to play in State of Origin football. However despite his good form, Brisbane were unable to win the Premiership, falling four points short of the Grand Final (losing the preliminary final to eventual premiers the Sydney Roosters by a scoreline of just 16-12).
At the time of his retirement, Langer had made the most appearances as captain for the Brisbane Broncos and became only the third player to have been named man-of-the-match in a State of Origin game more than three times.
After playing Langer spent time as a restaurateur on Queensland's Sunshine Coast. In 2003 Langer was one of the first four former players inducted into the Broncos official Hall of Fame. During the 2007 season at the Broncos' 20-year anniversary celebration, the club announced a list of the 20 best players to play for them to date which included Langer.
On 29 March 2010, Langer was charged with drink driving. At the time of the incident, Langer was ambassador for Lion Nathan brewery. He went to the Normandy Hotel in inner Brisbane, where he was photographed dancing in his underpants in front of patrons. Langer drank 8 to 10 glasses of beer and a couple of vodkas, before driving his car. He had intended to drive all the way to his home on the Sunshine Coast, but a police patrol pulled him over in the Brisbane suburb of Everton Park. The police found Langer to be 3 times over the legal blood alcohol limit. Langer pleaded guilty to the offence in Brisbane Magistrates Court. Lion Nathan cancelled Langer's brewery ambassadorship, and he was suspended from his coaching position with the Broncos. The court banned Langer from driving a motor vehicle for eight months. However no criminal conviction was recorded, as the judge accepted Langer's argument that a conviction would hurt his football coaching career. By the following weekend Langer had returned to work as Broncos assistant coach.