The 6-foot-10 Onuaku was a second-round pick by the Rockets in 2016 and played sparingly over two seasons. The Mavericks traded the rights to forward Maarty Leunen to the Rockets in the deal.
Onuaku averaged 3.0 points and 2.3 rebounds in six games with Houston.
The Mavericks also signed free agent guard/forward Ryan Broekhoff. The 6-7 Broekhoff spent the past five seasons playing professionally in Turkey and Russia.