The new parliament is expected to endorse personnel changes that observers say are likely to affect a number of officials linked to his "traitor" uncle Jang Song-Thaek, once the North's unofficial number two and Kim's political mentor.
Kim was reaffirmed as First Chairman of the powerful National Defence Commission (NDC) by the new parliament, in a show of "absolute support and trust of all service personnel and people in him", the Korean Central News Agency (KCNA) said.
Upon his re-election, "all the deputies and participants in the session broke into stormy cheers of 'hurrah!', extending the highest glory and warmest congratulations to him," KCNA said.
Kim also serves as first secretary of the ruling Workers' Party of Korea and supreme commander of the Korean People's Army, but his re-election as head of the top military body confers upon him ultimate power in the heavily militarised state.
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The session of the parliament, the Supreme People's Assembly, is being closely watched for glimpses into power shifts within the reclusive regime.
Kim led yesterday's meeting of the ruling party's high-level political bureau, which discussed "reinforcing" the party's organisation in order to boost its "leadership role and function", KCNA said, indicating personnel changes.
Today's opening parliamentary session comes after "elections" last month in which single candidates - approved by the political elite - stood uncontested. Kim notably managed a perfect turnout in his own constituency.
Several other elderly military leaders - such as defence minister Jang Jong-Nam and Ri Yong-Gil, chief of the military's general staff - are seen as likely to take seats at the NDC, replacing Jang and his suspected associate, former police chief Ri Myong-Su.