Supporters say the document approved by the People's Council will promote multi-party politics, as well as a market economy, the BBC reported Saturday.
After elections in December, the People's Council, a group of 2,500 tribal elders and local lawmakers, will dissolve, while Parliament will almost double in size, the British network reported.
The former Soviet nation adopted its constitution two years after the death of Saparmurat Niyazov, the autocrat whose power kept the Asian nation in isolation for nearly 20 years.
Niyazov's successor, President Kurbanguly Berdymukhamedov, said the country's former constitution was "outdated" and no longer fit with Turkmenistan.
"The new constitution corresponds to all international and democratic norms," he was quoted by BBC as saying. "By adopting it, we will show our country's authority at an international level."