Mr Pohiva, the eldest son of the late prime minister, 'Akilisi Pohiva, narrowly won the by-election for his father's former Tongatapu One constituency.
Sioasi Pohiva defeated scientist Netatua Pelesikoti Taufatofua by just 16 votes.
The win was an assurance that people still wanted to see a more democratic Parliament and more political reform, he said.
Mr Pohiva wanted to see the power of the nobility reduced, but he did not necessarily want their seats in Parliament to go.
He said there were several options available.
"There could still be the nobles' representatives but a system where this group, or class, co-exist, but still there is accountability to the people. Like the people electing the prime minister, would be an example of another option, instead of those being elected having the right to elect the prime minister."