The gathering on Monday afternoon will start from an assembly point at the square overlooking the site of the blast.
"The peaceful rally will lend support to the victims of the criminal act which targeted innocent individuals, and denounce all criminal acts," the Qatar News Agency (QNA) reported.
Saturday's blast that killed British expatriate Jonathan Adams, 40, was carried out by an Egyptian national who drove an explosives-laden car into a theatre where Adams was directing a play being performed by local group The Doha Players.
It was the first such bombing in the Gulf state, a close ally of the United States.
The Egyptian national has been identified as Umar Ahmad Abd Allah Ali, who had lived in Qatar for 15 years and worked as an information technology engineer for the state-run Qatar Petroleum (QP), company sources said.
Meanwhile, a previously unknown group claimed responsibility for the attack in a statement posted on the internet on Monday.
The group, calling itself Jund al-Sham Organisation, (Organisation of Soldiers of the Levant or greater Syria, referring to Syria, Lebanon, Jordan and Palestine), said in the statement that it would soon issue another release about "the martyrdom-seeking operation carried out by a lion from Jund al-Sham in Qatar".
Religious scholar Shaikh Yusuf
al-Qaradawi denounced the attack
There was no way to verify the authenticity of the statement, signed by the group's "military wing".
Doha-based Egyptian religious scholar Shaikh Yusuf al-Qaradawi denounced the attack in the gulf state.
"Islam strongly forbids the shedding of blood without a reason," al-Qaradawi told Aljazeera.net.
"We strongly condemn this act and condemn whoever did it," he added.
Al-Qaradawi also called on people in Qatar to unite against "these criminal acts so that they won't happen again".