Roy Bennett described his ordeal as "hell" and said inmates were beaten daily and kept barely clothed.
"I feel very sad for those that are left behind there ... because I should imagine if one gets to hell, that is what you experience," Bennett, a shrunken version of his normally burly self, told reporters at a news conference after his release.
Parliament voted to jail Bennett, then a legislator for the opposition Movement for Democratic Change (MDC), last October after he hit Justice Minister Patrick Chinamasa during debate on President Robert Mugabe's policy of seizing white-owned farms to give to landless blacks.
Bennett, a former farmer whose property had been confiscated, said at the time his actions against Chinamasa followed provocation and verbal abuse in parliament, which is dominated by Mugabe's ruling ZANU-PF party.
Chinamasa had called Bennett's forefathers "thieves and murderers" and said he deserved to lose his farm after benefiting from a British colonial system that robbed blacks of their land.
"I pushed him ... and for that I have spent eight months in jail under the most inhumane conditions. If that is justice, then so be it, but I certainly don't feel I deserved the sentence that I got," Bennett said.
The former coffee farmer was released from prison four months early under a system that allows lesser sentences for good behaviour.
"This was worse than anything I've heard of, or could have thought, to experience people being beaten on a daily basis, to hear their screams, to see people hardly clothed," he said.
Mugabe's government denies charges that inmates suffer abuse in its prison systems.
Bennett said he himself was stripped naked in front of guards and later given a filthy prison uniform covered with human excrement upon his initial admission into jail.
Last month Bennett appealed to the Supreme Court against his conviction and sentence, saying his case was conducted by a biased parliament which discriminated against him because of his race and political affiliation. The country's highest court had yet to make a ruling on the matter.
The MDC and several Western countries have criticised Zimbabwe's farm seizures, which the ruling party says are necessary to redress the ownership imbalances created by Britain's 1890's colonisation of the southern African state.
Bennett was one of three whites elected into parliament on an opposition ticket in 2000 parliamentary elections narrowly won by ZANU-PF. The MDC made a near clean sweep of urban centres, but Bennett's own victory was in a rural constituency traditionally the preserve of the ruling party.
Bennett's wife, Heather, stood for the MDC on his behalf in this year's general polls held on March 31, but lost the Chimanimani seat in eastern Zimbabwe to her ZANU-PF opponent.
Heather Bennett is among several MDC candidates who have launched court challenges to their defeat at the polls, which the MDC says were rigged. ZANU-PF denies the charge.