Even if the motion passes, its economically and militarily more powerful neighbour South Africa - which completely envelops Lesotho - is unlikely to cede the land.
To do so would violate an agreement between African countries in the 1960s to respect the borders laid down by colonialists during centuries of exploitation of the continent.
It suggests that Lesotho should reclaim all of Free State province, which at 130,000 square kilometres is more than four times the size of the kingdom, as well parts of four other provinces bordering the landlocked state.
Large parts of the population in these areas are from the same Basotho nation which also makes up Lesotho's 2 million-strong population. In fact, there are around twice as many Basotho in South Africa as in Lesotho.
The motion was brought by Tsepo Lipholo, a minor opposition leader who occupies the opposition Basotho Convenient Movement’s only seat in the 120-seat parliament.
"History has a record of what was taken from our people and that people were killed in the process. It is time to correct that," he told parliament on Wednesday.
"It's time for what is ours to be returned to us".
Historically, the seizure of Basotho land by Dutch settlers - whose descendents, Afrikaners, now own most of the land in Free State - is well-attested.
Lesotho became a British protectorate in 1868, after the then king Moshoeshoe I appealed to British imperial authorities to prevent any more land being seized. The borders of current-day Lesotho were established by a treaty signed between Britain and the Dutch settlers the following year, and it was later annexed and then run by Britain until independence in 1966.
Lipholo promised to reclaim these lost territories in his election campaign last year last year.
He bases his case on a 1962 United Nations resolution that recognised the right to self-determination and independence for the people of Basotholand.
Unlikely. The motion to return the land is not especially popular amongst the inhabitants of Lesotho, who are more concerned with economic problems like widespread poverty, unemployment and crime.
Even though the issue emerges periodically as a talking point, it doesn't appear to have the majority support in parliament necessary to become a law.
In the 1964 Cairo Declaration by the Organisation of African Unity (now the African Union), African leaders agreed that their newly independent countries will recognise the borders inherited from colonial powers to avoid stirring future conflicts - so South Africa has a strong case to reject any claim from its neighbour.
Eswatini's King Mswati III has in the past similarly claimed that big parcels of neighbouring South African land were historically part of his kingdom and should be returned, but has never realised them.
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