A local immigration official was among those given death sentences, while an army colonel was given 10 years in prison, said Tresor Kabangu, who represented several defendants in the trial.
Congo has observed a moratorium on the death penalty since 2003, so those convicted will serve life sentences.
But Human Rights Watch's senior researcher on Congo, Thomas Fessy, and Catalan's sister said investigators had ignored the potential involvement of higher-level officials and the trial had not revealed the truth.
Catalan, a Swede, and Sharp, an American, were investigating violence between government forces and a militia in the central Kasai region in March 2017 when they were stopped along the road by armed men, marched into a field and executed.
Congolese officials have blamed the killings on the Kamuina Nsapu militia. They initially denied any state agents were involved but later arrested the colonel and several other officials who they said were working with the rebels.
After a nearly five-year trial marked by repeated delays and the deaths of several defendants in custody, a military court in the city of Kananga delivered its verdict on Saturday.
Among those sentenced to death was Thomas Nkashama, a local immigration official who met with Catalan and Sharp the day before their fatal mission, Kabangu told Reuters. Others were alleged members of the militia.
Colonel Jean de Dieu Mambweni, who also met with Catalan and Sharp before their mission, was sentenced to 10 years, Kabangu said.
A number of the defendants were convicted in absentia because they were either never apprehended or escaped from custody.
Catalan's sister, Elisabeth Morseby, said after the verdict that testimony in the case was of dubious reliability given how much time the defendants had spent together in prison and said the conviction of Mambweni was a smokescreen.
"In order for the truth to emerge, all suspects, including those higher up in the hierarchy, need to be questioned, which has not yet been done," she told Reuters.
Congo's chief military prosecutor was not immediately available for comment. Prosecutors have previously said that they followed the available evidence.
Fessy said there were still more questions than answers after the verdict.
