Pakistan's de facto interior minister, a close aide to President Asif Ali Zardari, was Friday sworn back into parliament just weeks after being forced to step down over his alleged British citizenship.
The swearing-in ceremony was broadcast live on state television.
The Supreme Court suspended Malik from parliament on June 4 for allegedly running for the Senate in 2009 while still holding British citizenship.
The Pakistani constitution bars MPs from acquiring foreign nationality.
Documents that Malik submitted to the court failed to convince judges that he had renounced his dual nationality before being elected.
Under the constitution, only members of parliament can hold the rank of cabinet minister.
After his suspension, Malik was swiftly appointed the prime minister's "advisor" on interior affairs, effectively allowing him to keep his interior ministry job.
The by-election was held in Karachi, a stronghold of Zardari and his Pakistan People's Party (PPP), although Malik is originally from the central province of Punjab.
The Karachi seat won by Malik is reserved for technocrats. Malik is a former official from the Federal Investigation Agency.
The Supreme Court has recently suspended a number of MPs over dual nationality, including Farahnaz Ispahani, an advisor to Zardari and the wife of Pakistan's sacked ambassador to Washington. She holds dual Pakistani-US nationality.
Reacting strongly over Rehman Malik’s appointment as Senator, (PML-N) Friday staged a walkout from the Senate to protest what they said flouting of the apex court's orders by the PPP-led government.
PML-N under the vibrant leadership of Raja Zafar-ul-Haq, walked from the stormy session.
PML-N was of a clear stance that the senate session was an unscheduled one and has no record in the present parliamentary calendar in this regard.
The House Business Advisory Committee also had similar reservations on the Senate Session.
On the other hand, Jahanghir Badar made it clear to the angry senators that that the Senate Session was not called for oath taking ceremony of newly elected member of the House Rehman Malik.
He said that President of Pakistan address to the joint session of the parliament on March 17, 2012 was not completed hence its completion was mandatory. The Session was called for this purpose.
He further added that whenever President summons session, it can be called he has all the powers to do so in this regard.