Delivering the long-awaited verdict on Friday, justice Jessie Lessit singled out Leliman for acting "in flagrant abuse of his office" as a police officer and masterminding the murder.
Leliman's former colleagues and co-accused Stephen Cheburet Morogo and Sylvia Wanjohi who were also found guilty of the murder have been sentenced to 30 and 24 years respectively.
At the same time, their informant who is believed to have facilitated the execution of the brutal nurder of the three was sentenced to 20 years in prison.
Justice Lessit said the killing of Lawyer Willie Kimani, his client Josephat Mwenda and driver Joseph Muiruri was "a most foul murder, an execution that was most heinous."
The accused have 14 days to appeal the ruling.
The prosecution produced in court 46 witnesses to testify against the accused persons who in their defence brought forth 36 witnesses to defend them from the charges.
Lawyer Willie Kimani, his client Mwenda and the taxi driver were abducted after leaving Mavoko Law Courts in Machakos County on June 23, 2016. They were leaving a court session in Mavoko where Mwenda had filed a case against Fredrick Leliman.
The three were bundled into a vehicle and taken to Syokimau Police Post where they were locked up before they were later smuggled out and driven to a location where they were brutally murdered.
Their lifeless bodies were stashed in sacks and transported to a river in Ol Donyo Sabuk where they were dumped only to be recovered a week later on June 30 and July 1, 2016.