Who was the nationalist leader who led Laos with the move towards independence?

Prince Souvanna Phouma was the nationalist leader who led Laos with the move towards independence.

Which political party does he belong to or operates under?

Prince Souvanna Phouma was a key member of the Neo Lao Issara (Free Laos) movement, which was a nationalist political party that advocated for Laos' independence from French colonial rule.