The second assembly session in two months came amid growing momentum in the international community to punish Pyongyang for the sinking of a South Korean navy ship in March that killed 46 sailors.
Jang, who had once fallen out of Kim's favour but has since returned to his inner circle, is the husband of the leader's sister, and is viewed as the key figure for ensuring a smooth transfer of power from Kim to one of his sons.
"Jang would be the most trustworthy person to Kim who can establish the foundation for succession to Jong-un," said Park Young-ho of the Korea Institute for National Analysis.
"This is a signal that they will be moving on existing power structures, no innovation or openness or reform."
The parliament also sacked the country's premier, who is considered the top economic official, and replaced him with Choe Yong-rim, a member of the old guard and another confidant of Kim's family who has been in key economic posts.
The dismissal of Premier Kim Yong-il is likely linked to a currency revaluation late last year that, according to some media reports, incited widespread public discontent.
Kim, who suffered a stroke in 2008, missed the previous session of the Supreme People's Assembly in April, which amended the country's constitution to strengthen his power.
Some analysts suggested Pyongyang might use the occasion to issue a rebuttal of sanctions imposed by the South over the sinking of the Cheonan corvette.
However, there was no mention of any hardline response to the latest actions by South Korea, which last week took the dispute to the UN Security Council, demanding that the North admit to the attack.
The mounting antagonism between the two Koreas, which so far has remained rhetorical, has unnerved global investors, worried about armed conflict breaking out in a region home to the world's second and third biggest economies.
The South Korean and US military are expected to stage a joint exercise later this month, postponed from this week, to test their readiness against aggression from the North.