Ilhan Omar, 34, who wears the hijab, was elected to serve in Minnesota's state house of representatives.
The Muslim Somali-American woman becomes the highest-ranking Somali elected to office in the US.
Her election comes just days after US President-elect Donald Trump accused Somali immigrants in Minnesota of "spreading their extremist views".
Minnesota has the nation's largest Somali community - about 50,000 according to the US census.Celebrating her victory, Ms Omar said she would be the "voice for the marginalised" in the state parliament.
"I think I bring the voice of young people. I think I bring the voice of women in the East African community. I bring the voice of Muslims. I bring the voice of young mothers looking for opportunities," Minnesota Public Radio quoted her as saying.
According to the bbc.com Ms Omar escaped from Somalia with her family at the start of the civil war when she was eight years old.
They lived in a Kenyan refugee camp for four years, before moving to the US and settling in a Somali-American neighbourhood in Minnesota.