The southern African country heads to the polls on August 23 to elect the president and legislature in what analysts expect to be a tense affair, marked by a crackdown and fears of rigging.
"Zimbabwe's authorities have yet again demonstrated a lack of respect for the basic freedoms necessary for a credible, free, and fair election," said HRW's senior Africa researcher, Idriss Ali Nassah.
The United States-based rights group said the authorities had adopted repressive laws to muffle dissent and used intimidation and violence against the opposition.
The courts have been "weaponized" to target opposition politicians, while the election overseers lack impartiality, the group said in a report based on interviews with activists and politicians.
"The Zimbabwe government needs to take concrete measures before the election to meet its obligations under national and international law to allow people to vote free of intimidation, fear, and violence," Nassah said.
"So far nothing indicates the authorities are willing to do that."
Zimbabwe's government did not immediately reply to a request for comment.
President Emmerson Mnangagwa, 80, who heads the ZANU-PF in power since independence in 1980 and forced out late ruler Robert Mugabe in 2017, is seeking re-election.
His main challenger is Nelson Chamisa, a 45-year-old lawyer and pastor.