Both nations have the chance to reach the showcase tournaments held in 2020, with ZC yet to be reintegrated after their membership was revoked by the ICC
Namibia and Nigeria will have the chance to reach their first-ever World T20 after being confirmed to replace Zimbabwe in the qualifying competition for the women and men's tournament.
Zimbabwe Cricket have breached rules over governmental interference, according to the ICC, and have had their membership suspended until their board has been fully reinstated.
All teams have therefore been blocked from future events, which had led to a change in the line-up for the two upcoming qualifying events.
Eight teams will battle it out for two berths in the women's tournament in a qualifying competition held across August and September.
And it is Namibia who have been selected to replace Zimbabwe having lost to The Chevrons in the final of the Africa pathway.
"It feels like we're political pawns in their chess game" - The human impact of Zimbabwe's suspension
They join hosts Scotland, Bangladesh, Ireland, Netherlands, Papua New Guinea, Thailand and USA in pursuit of the last two places.
The Women's World T20 is scheduled to take place between February 21 and March 8 2020 in Australia.
October and November will see the men's qualifying tournament contested between 14 nations in the United Arab Emirates.
Nigeria finished third behind Namibia and Kenya in regional qualifying and thus replace Zimbabwe as the third direct entrant to hail from Africa.
Comprising as 16 teams for the first straight edition, the Men's World T20 will be held between October 18 and November 18 2020, also in Australia.