An anti-graft court found Sadeque Hossain Khoka, now living in the United States, guilty of amassing wealth illegally and of concealing information about his income.
"He was sentenced to 13 years in jail in total for the two charges," Mosharraf Hossain, prosecutor for the country's Anti Corruption Commission, told AFP.
"The judge also ordered confiscation of 100.5 million taka (USD 1.3 million) in illegally acquired property," he said.
He now lives in New York where he is being treated for cancer, his lawyer Sanaullah Mian told AFP, adding that they planned to appeal against the verdict.
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Mian, who is also a BNP official, called the case "one hundred percent politically motivated".
"It is part of the government's repression of the opposition," he said.
The BNP and its Islamist allies have accused the government of Prime Minister Sheikh Hasina of cracking down on the opposition in recent months after they tried to topple her through a violent transport blockade early this year.
Last month Zia left the country for London for treatment for eye and knee problems, with some speculating that she might not return to the country in an attempt to avoid imprisonment.