Ouahim joins the A-League Men club on a two-year deal, making the overseas move after five appearances on-loan for Moldovan Super Liga club Sheriff Tiraspol.
The attacking midfielder began his career with two-time Bundesliga champions Koln FC in 2017 and spent five years in the German league, before making the switch to Dutch second-tier club Heracles Almelo.
Brought to Sydney to be a playmaker, Ouahim will most likely line up in the No.10 role, but has played on the left wing.
"I had the feeling that they really want me because they knew that I'm a good pressing player," the 26-year-old said on Tuesday.
"They saw that I'm defensively against the ball and pressing a good player that can take the ball.
"That's one of my qualities, and I was happy to hear that they knew it."
A playing career in the Australian league had never crossed his mind until the club had approached him, leaving Ouahim without any doubts.
Such was his enthusiasm he drove from the Netherlands to Germany in a bid to fast track his visa process.
"In Germany, they are very slow ... so they told me it's going to take one to four weeks," Ouahim said.
"I said 'No, I can't accept that. I want to be earlier there' so I drove some hours to make it happen."
Ouahim is the second off-season signing under Sydney coach Ufuk Talay, following Australian goalkeeper Harrison Devenish-Meares.
The club is still on the lookout for a striker and a defensive midfielder following the departure of big-name players including Fabios Gomes, Luke Brattan, Robert Mak, Jack Rodwell and Jake Girdwood-Reich.
Nisbet leaves treble winners Central Coast after declining an upgraded offer from the club to pursue a stint abroad.
Josh Nisbet's time with Central Coast Mariners is over as he seeks a new club overseas. (Dan Himbrechts/AAP PHOTOS)
The move comes after seven years with the Mariners and a career-best season, with Nisbet capping the 2023-24 campaign with the Johnny Warren Medal, awarded to the league's best player.
He missed just 28 minutes across 44 games, won two PFA Player-of-the Month awards and was named in the PFA Team of the Year, finishing with the most assists in the competition.
Nisbet was rewarded with his first Socceroos call-up, making his international debut against Lebanon in March.
Meanwhile, fellow German midfielder Tolgay Arslan has quit Melbourne City despite being signed for at least one more season and having attended pre-season training.
The 33-year-old asked for an early release, a request "reluctantly" agreed to by the club.
His departure deals a significant blow to City, who lost league record goal-scorer Jamie Maclaren in April.
Arriving in June 2023, Arslan took out the club's Player of the Year award and the Players' Player Award after scoring 19 goals and providing seven assists in 34 appearances across all competitions.
The Club has reluctantly agreed to the mutual termination of Tolgay Arslan's contract.— Melbourne City FC (@MelbourneCity) July 9, 2024
Also on Tuesday, goalkeeper Paul Izzo left Melbourne Victory.
Izzo has joined Danish club Randers off the back of two standout seasons in Melbourne, with Victory netting a small transfer fee for the 29-year-old shot-stopper.
The club will at least be able to rely on the services of defender Jason Geria, who signed a two-year deal.
Across the Tasman, Wellington announced the re-signing of Marco Rojas for next season, while ex-Victory playmaker Jake Brimmer joined newcomers Auckland FC.
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