Commentators have described the development as an ironic and dramatic twist of events for a politician who is disputing the presidential result, seeking nullification from the constitutional court, which is set to begin hearing the case from this Wednesday.
A panel of five judges from the constitutional court will hear the case.
President Professor Arthur Peter Mutharika was declared winner by the Malawi Electoral Commission (MEC), after be cruised to victory with over 150,000 votes in first-past-the-post presidential system.
A social commentator said it was a "big surprise" to see Chakwera being sworn in as opposition MP while he rejects the results of the presidential contest which he lost to Mutharika. " I thought he was going to seek nullification of the parliamentary poll as well. It means he accepts both results."
Chakwera begun his political journey as a presidential candidate in 2014 and failed to to win, coming second to Mutharika. The then incumbent president Joyce Banda came third.
A former head of the Assemblies of God Church in Malawi, Chakwera was opposition leader in parliament since 2014.
The DPP has scooped 62 seats in the May 21 poll, while MCP got 55 seats. The House will haave 55 independents, while UTM have a paltry 4 lawmakers.
Mutharika, who started his last term as President last month after being sworn in at the Kamuzu Stadium in Blantyre by Chief Justice Andrew Nyirenda, will officially make his state of the nation address to parliament on June 21 when he is expected to outline his development agenda for the next five years.