Sri Lanka's new parliament opened its first session Thursday with a murderer and an accused killer among its ranks after a sweeping election victory by the ruling Rajapaksa brothers.

One member of the legislature was convicted of murder only after nominations closed for the August 5 polls -- allowing him to run for a seat -- while another is awaiting trial.

Premalal Jayasekara, a returning MP from Prime Minister Mahinda Rajapaksa's Sri Lanka Podujana Party (SLPP), was found guilty in the killing of a political activist in 2015.

Jayasekara -- who did not appear in person for the first parliamentary session -- is appealing against the verdict as well as a death sentence he was handed.

He is the first convicted murderer to serve as an MP in Sri Lanka, where there is no provision under the law to disqualify him until he serves six months behind bars.

Sivanesathurai Chandrakanthan, in parliament for the first time after winning a seat for a minor party in an alliance with the SLPP, was escorted from prison to attend Thursday's parliamentary session.

He is awaiting trial for allegedly killing a legislator during a 2005 Christmas mass.

Maintaining the two-thirds majority in parliament that the SLPP secured in the recent election is crucial for Mahinda and his younger brother and President Gotabaya Rajapaksa.

The SLPP won 145 seats in the poll and can also count on at least six allies in the new 225-member legislature, according to Election Commission results.

The brothers need at least 150 seats to overturn reforms limiting executive power made by a previous administration so they can expand their grip on power.

Gotabaya -- who is directly elected by voters and is not an MP -- will address the legislature later Thursday when he is expected to unveil his policies.

Brushes with the law are no bar to a career in politics in South Asia.

More than 40 percent of lawmakers in neighbouring India's parliament face criminal charges -- some as serious as murder and rape –- according to an electoral reform group, the Association of Democratic Reforms.