"Some of the suspects, in their statements recorded by police officers, confessed to have taken part in the conspiracy meetings and in killing," the judge, Laila Mgonya, told the court.
"The evidence provided was strong enough to convict them."
Anti-poaching activist Wayne Lotter, a South African national, was shot dead in August 2017 while riding in a taxi in Tanzania's commercial capital of Dar es Salaam.
Those sentenced to death include nine Tanzanians and two citizens of neighboring Burundi.
Tanzania hasn't carried out an execution in decades. The last execution carried out in the country was in 1994.
Lotter was the director and co-founder of the PALMS Foundation, a nongovernmental organization which said he had helped to train thousands of game scouts throughout Tanzania and developed an “intelligence-based approach” to anti-poaching that had success in countering wildlife trafficking.
Poachers in Tanzania target various wildlife, including elephants that are often killed for their tusks.
Some information for this report came from Agence France-Presse.
