The Truth and Reconciliation Commission on Wednesday rejected the pair's application for amnesty for the murder - the main finding that they had failed to prove the killing was politically motivated.
The TRC's amnesty committee also found that the men had failed to make a full disclosure, another prerequisite for amnesty.
Political parties on the right of the political spectrum slammed the ruling.
Polish immigrant Walus and former Conservative Party parliamentarian Derby-Lewis had tried to prove to the TRC's amnesty committee that they had taken their cue from the CP in killing the general secretary of the SA Communist Party.
But the committee said it was "common cause that the applicants were not acting on their express authority or orders from the Conservative Party which they purport to represent in assassinating Mr Hani".
Evidence by current CP leader Ferdi Hartzenberg that violence was not part of the CP's policy "negated any claim that the public utterances of the CP leadership constituted implied authority for the assassination".
The committee also rejected Walus' claim that he had acted on Derby-Lewis' orders.
"Walus was under no duress or coercion and executed the plan as he deemed fit," the committee said.
"He (Walus) had a clear understanding of the political situation and was active in rightwing politics. He participated fully in political discussions and hatching the plot to assassinate Mr Hani."
The committee picked on the apparent contradiction between Walus' and Derby-Lewis' testimony on the planning of the murder.
The committee also said the men had not fully disclosed information about the nature of the "hitlist" found in Walus' possession after the murder, and the circumstances surrounding the acquisition of the murder weapon.
The only finding the committee made on the role of Derby-Lewis' wife Gaye in the murder, was that she had prepared the hit list.
The amnesty committee said that while there were "compelling arguments" in favour a wider argument to kill Hani, it could find no conclusive evidence to prove this.
Walus shot and killed Hani in the driveway of his home in Dawn Park, Boksburg, on April 10, 1993.
He and Derby-Lewis were subsequently convicted and sentenced to death. But their sentences were rendered invalid when capital punishment was declared unconstitutional by the Constitutional Court in 1995 and abolished.
Their fate now lies with in the hands of the courts and the country's President. In terms of the Criminal Law Amendment Act 105 of 1997, they must return to the court where they were originally sentenced for a new sentence to be passed, according to chief state law adviser Enver Daniels.
The president must approve the new sentences.
The act specifies that life imprisonment should be imposed for certain serious crimes, including planned or premeditated murder. There is no option for appeal against such sentences.
Derby-Lewis' wife, Gaye, expressed shock at the committee's decision but said her husband's lawyers were examining the possibility of challenging the commission's ruling in court.
"We certainly are not going to take the decision lying down."
She said she visited her husband in the morning after he received the news on his amnesty application.
"He is bearing up very well, and nothing will get him down. He is a brave man."
Walus was divorced from his estranged wife Wanda last year and recently applied to marry Berril Roy, his girlfriend of three years, in prison. The Department of Correctional Services has since clamped down on prison marriages.
CP leader Hartzenberg said the timing of the announcement by the TRC was politically motivated because the ANC stood to benefit from the move.
The decision comes in the run-up to the June 2 election, and could be used as election propaganda by the ANC, which hoped to achieve a two-thirds majority, he said. It also coincided with the commemoration of Hani's death in three days' time.
The Freedom Front said it was "a shame" that Walus and Derby-Lewis were not granted amnesty because Hani had a high political profile and had been killed because of his political connections.
FF justice spokesman Rosier de Ville said that if amnesty was given to the Azanian People's Liberation Army operatives who killed innocent members of the congregation of St James church in Cape Town, who had no political connection, it should surely be given to Walusz and Derby-Lewis.
The New National Party said the TRC had been inconsistent in its amnesty decisions, possibly because of political pressure.
"The danger exists that the Amnesty Committee may be tempted to apply different norms and standards depending on who the applicants are and what the political pressures may be," NNP spokesman Jacko Maree said.
Maree, however, declined to say whether his party approved or disapproved of Wednesday's ruling.
ANC spokesman Smuts Ngonyama said the men deserved to stay in jail for the rest of their lives because what the two men stood for had been "totally barbaric and immoral".
The SACP, which joined Hani's family in opposing amnesty for the men, said the two men had been sparing with the truth, evasive and often arrogant, and the party was convinced they had failed to meet any of the criteria for amnesty.