Niemann is renowned for his successes various national and international chess tournaments. Notable instances include his victory at the 2019 North American Junior U20 Charity Chess Championship, and subsequent achievements at the 2020 Charlotte Labor Day Chess GM Norm Invitational. Niemann also won the 2021 U.S. Junior Championship.
Outside of playing, Niemann is known as a chess promoter and popularizer. He runs the Twitch channel ‘gmhans’, where he plays chess and interacts with viewers. This includes discussing strategies and variations, answering questions, and providing analysis of his games. Niemann has a large following on this platform. He also maintains an active profile on various other online chess platforms.
Niemann is also actively engaged in community services. For example, Niemann donated the prize money of the 2019 North American Junior U20 Championship (Over $1,200) where he came first, to the University of Maryland Children's Hospital.