Ardern, who was the only Kiwi on the list, placed higher than Hillary Clinton, who was ranked as the 20th most powerful woman.
Together, the 22 women directly influence more than 3 billion people, according to Moira Forbes, executive vice-president of Forbes Media.
"Whether leading multibillion-dollar companies, governing countries, transforming an industry, or setting the agenda on critical issues of our time, collectively these women are making a lasting impact on our global footprint," she told The Guardian.
Forbes said Ardern "surged to power in New Zealand on a wave of voter excitement dubbed 'Jacindamania'".
Ardern's partner Clarke Gayford tweeted a message of support following the announcement.
"You think I'm proud? The bloody cats now strutting around the house like she's Simba."
Donald Trump's daughter Ivanka was named the sixth most powerful woman for her role as senior adviser to her father.
Angela Merkel remains the most powerful woman in the world, while the British prime minister, Theresa May, took out second place.
Forbes' 22 Most Powerful Women In Politics:
1: Angela Merkel, Chancellor Germany
2: Theresa May, Prime Minister, U.K.
3: Tsa Ing-Wen, President, Taiwan
4: Michelle Bachelet, President, Chile
5: Federica Mogherini, Foreign Policy Chief, European Union
6: Ivanka Trump, Senior Advisor, The White House
7: Ruth Bader Ginsburg/Elena Kagan/Sonia Sotomayor, Supreme Court Justices
8: Queen Elizabeth II
9: Sheikh Hasina Wajed, Prime Minister, Bangladesh
10: Beata Maria Szydlo, Prime Minister, Poland
11: Aung San Suu Kyi, State Counsellor, Myanmar
12: Sheikha Lubna Al Qasimi, Minister of International Cooperation & Development, U.A.E.
13: Jacinda Ardern, Prime Minister, New Zealand
14: Kolinda Grabar-Kitarovic, President, Croatia
15: Nicola Sturgeon, First Minister of Scotland, U.K.
16: Nikki Haley, Ambassador to United Nations, U.S.
17: Erna Solberg, Prime Minister, Norway
18: Elvira Nabiullina, Governor, Bank of Russia
19: Liyuan Peng, First Lady, China
20: Hillary Clinton, Former Presidential Candidate, U.S.
21: Dalia Grybauskaite, President, Lithuania
22: Kersti Kaljulaid, President, Estonia