Washburn joins fellow Americans Xavier Thames and Winston Shepard on the Rams’ squad.
The 26-year-old Washburn will arrive in New Zealand on Thursday after winning the NBA G-League championship with the Austin Spurs, the developmental affiliate of the San Antonio Spurs.
He compiled averages of 5.0 points and 3.2 rebounds in 24.2 minutes per game (50 games) for Austin, shooting 43.0 per cent from the field and 37.4 per cent from three.
Washburn attended the University of Texas at El Paso (UTEP) for four years and earned Conference USA Defensive Player of the Year honors in his senior season.
He instantly becomes one of the best defensive players in the NBL, and will complement the likes of Thames and Shepard well, both of whom are primarily skilled on the offensive side of the ball.
The Rams’ season begins on April 27 against the Super City Rangers.