Alexander's bright career began in Ryde East Primary School and Epping Boys' High School where he showed excellent talents on the field as a sportsman and off the field in his sportsmanship. His main junior football club was North Ryde and then with Gladesville Hornsby/Northern Spirit youth team where he played alongside Brett Holman. Two years after breaking into the first team of the Northern Spirit, the NSL would be shut down and went back to finding a job, where he would eventually work at a surf shop in his local Macquarie Centre. On Sunday 12 November 2006, Noel Spencer was dropped from the starting eleven and in his absence Alex Wilkinson was named captain of the team. Spencer was then struck down with injury and Alex filled in as captain until round 18 when Spencer returned. He was named Captain for Season 3 and only injury has interrupted that. On 17 March 2011 it was announced that Wilkinson had signed a short-term loan deal with Chinese side Jiangsu Sainty. On 18 July he had signed a two and a half year contract with K League 1 team Jeonbuk Hyundai Motors. The reported transfer fee paid to the Mariners upon completion of the deal is $450,000. Following a lengthy and successful stint in Asia, Wilkinson signed with Melbourne City in February 2016, for the remainder of the 2015–16 A-League season.
Sydney FC
After Melbourne City were eliminated from the finals series Wilkinson signed a two-year contract with Sydney FC, rejoining former Mariners manager Graham Arnold In 2017, Wilkinson made sporadic appearances as captain on the pitch with skipper Alex Brosque off and vice-captain Sebastian Ryall injured for the majority of the season. In July 2019, following the retirement of captain Brosque and after spending 3 years as vice-captain, Wilkinson was appointed captain of Sydney FC.
International career
He represented Australia in 2003 FIFA World Youth Championship. In August 2006, Alex was selected for the first time to join the 22 man Socceroos squad, training for the Asian Cup against Kuwait. He has also joined the 37 man training squad for the Socceroos against Qatar. He made his full national team debut against Ecuador in a friendly at The New Den in London on 5 March 2014. He was a surprise inclusion for Australia's 2014 World Cup squad and started in Australia's 3–1 opening loss to Chile. After he cleared a certain goal off the line he was the first player in history to be involved in FIFA's new goal line review system which showed he successfully saved a goal. On 30 March 2015 in a friendly match against FYR Macedonia, at the 72nd minute as captain Mile Jedinak was substituted off the ground, Wilkinson was handed the captain's arm band.
