In a statement signed by Sibghatullah Mojaddedi, the chamber's chairman, the Senate also condemned what it called "international interference" to have the sentence annulled, spokesman Aminuddin Muzafari said.
The journalist, 23-year-old Sayed Parwez Kaambakhsh, was sentenced to death last week by a three-judge panel in the northern city of Mazar-i-Sharif for distributing a report he printed off the Internet to journalism students at Balkh University.
The article asked why men can have four wives but women can't have multiple husbands.
The court in Mazar-i-Sharif found that the article humiliated Islam. Members of a clerical council also pushed for Kaambakhsh to be punished.
"That issue was not in the (Senate's) agenda, but when lawmakers gathered on Tuesday they insisted on talking about that case," Muzafari said.
Following a debate, lawmakers decided to issue the statement supporting the court's decision, he said.
Kaambakhsh has appealed his conviction and the case will now go to an appeals court. President Hamid Karzai will have the final say in the matter.
International human rights groups have condemned the sentence and called on Afghan authorities to quash it.