The 80-year-old leader, who is seeking re-election, urged Zimbabweans to "say no to violence, before, during and after" the upcoming vote.
"My government has put measures in place to ensure free, fair and credible elections", he said in a speech delivered at an event to mark 43 years of independence from Britain.
Mnangagwa also warned of "voices, foreign or local, inclusive of rogue NGOs" sowing "seeds of division and disharmony among us".
In early February the country's parliament approved a bill banning civil society organizations from engaging in politics.
Under the new legislature, the state can intervene in the governance and activities of charities and civil groups, including making changes to their internal management and funding.
The law, which caused outcry from rights groups and the global community, states that violators would risk up to a year in jail.
The southern African country is due to hold presidential and legislative votes, expected to be in August, but no date has been announced yet.
Mnangagwa's Independence day celebrations were held in the small town Mount Darwin, around 155 kilometers northeast of the capital Harare.
In 2018 Mnangagwa won disputed elections that his main rival Nelson Chamisa insists were rigged.
The two will face off for a second time in the upcoming polls.
Nicknamed "the Crocodile" for his ruthless cunning, Mnangagwa replaced strongman ruler Robert Mugabe in 2017 after a military-led coup.
He faces widespread discontent as he struggles to ease entrenched poverty, end chronic power cuts and crippling unemployment.