"Chamisa has been nominated as the )Citizens Coalition for Change (CCC) presidential)candidate by all streets and villages", the committee's spokesman Shepherd Ngandu told a press conference in Harare.
The opposition party has accused the president of a crackdown on political opponents.
Some of the CCC's campaigns have been blocked by the ruling party and the police.
There have also been widespread arrests of key opposition party officials.
Chamisa last week took to Twitter to accuse the government of "weaponization of the law" and "unjustly" incarcerating firebrand CCC lawmaker Job Sikhala, who has been held in a maximum security prison in since June.
He was arrested alongside the party's spokeswoman Fadzayi Mahere, who was convicted of publishing falsehoods last week.
Chamisa said on Twitter Mahere's conviction was "evidence of the increasing attacks on democratic forces in Zimbabwe", which he said needed "fixing".
Mnangagwa, known as "the Crocodile" for his ruthless cunning, faces widespread discontent as he struggles to ease entrenched poverty, end chronic power cuts and economic hardship.
In their initial face-off in 2018, Mnangagwa narrowly won the landmark election over Chamisa with 50.8 percent of the vote.
Chamisa is Mnangagwa's Election Rival
Citizens Coalition for Change Leader Mr. Nelson Chamisa
HARARE - Nelson Chamisa, a 45-year-old lawyer and pastor, will be Zimbabwean President Emmerson Mnangagwa's official opponent for a second time in an upcoming crunch vote, the opposition party confirmed on Thursday.