Willem Oosthuizen and Theo Martins Jackson, who both shifted nervously in the dock, laid their heads on the bench after their sentencing while female family members wept in the public gallery.
"The conduct of the accused was most dehumanising and disgusting," said judge Segopotje Mphahlele, handing down sentence in the High Court sitting in Middelburg, 165 kilometres east of Johannesburg.
They had pleaded not guilty over the incident last year in the eastern province of Mpumalanga, saying they only intended to scare Victor Mlotshwa whom they accused of stealing copper cables from their farm.
Oosthuizen, 29, was sentenced to a 16-year term with five years suspended, while Jackson, 30, was jailed for 19 years, with five also suspended.
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"The most appalling act of the accused was to put the complainant in a coffin against his will," said Mphahlele.
"Whilst in the coffin they threatened to set it alight. They asked him how he wanted to die -- quickly or slowly."
The judge said it was not the first time that the men had forced someone into a coffin against their will, saying their behaviour "raised and fuelled racial tension" in South Africa.
A lawyer for the men, Wayne Gibbs, called the jail terms "shockingly inappropriate," arguing that they were a result of intense media attention and public pressure.
Two clips of footage taken on their mobile phones showed the assailants shoving Mlotshwa down into the wooden coffin and pressing the lid closed with their boots as he begged for mercy.
When the first phone footage emerged several months ago, it triggered national outrage and led to the arrest of the two men.
"Please don't kill me," Mlotshwa begged the men while in the coffin, the footage showed.
Throughout the case, the men denied that their actions had caused the victim to fear for his life.
"The evidence of the accused and the conduct of the accused during their trial clearly displays a lack of remorse," said Mphahlele.