Melbourne Victory On 27 February 2017, Theoharous signed with
Melbourne Victory FC as a scholarship player, after having been part of the Victory's youth team since 2014. Theoharous made his Victory debut in 2017 as an 83rd minute substitute for
Daniel Georgievski in a 1–0 loss to
Brisbane Roar. Theoharous scored his debut first team goal for the Victory against the
Central Coast Mariners on 18 March 2018. Despite becoming a regular first-team player in the 2017–18 season, he missed Victory's
victorious Grand Final finish to the season after getting injured in the semi-final.
Borussia Mönchengladbach Borussia Mönchengladbach announced that he had signed for the club on their official website on 18 May 2018. Theoharous spent three seasons at the club, playing for their reserve team in the
fourth tier of German football, before he was released by Borussia Mönchengladbach in June 2021.
Western United On 1 November 2021, Theoharous joined Australian
A-League Men club
Western United on a two-year scholarship deal. Theoharous made 4 league appearances for Western United before the club and player agreed to a mutual termination of his contract on 17 January 2023, midway through the second season of his two year deal.
Central Coast Mariners In January 2023, after agreeing a mutual termination of his contract with
Western United, Theoharous signed with
Central Coast Mariners until the end of the season, with an extension option. Theoharous made his debut for the club at the first game since his signing, appearing off the substitute's bench against
Wellington Phoenix. Theoharous was part of the 2022-23 A-League Championship winning team for the Mariners, in his first season at the club. Midway through the 2023-24 season, Theoharous signed a one-year contract extension. Theoharous was part of the Mariners' Championship, Premiership and
AFC Cup winning
2023-24 season. ==Career statistics==