Aregawi, 23, who moved to Sweden in 2009 and took Swedish citizenship in June 2012 but was not cleared to run by the IAAF until December of that year, clocked 4min 00.61sec.
Ethiopian Axumawit Embaye took silver in 4:07.12, with Canada's Nicole Sifuentes claiming bronze (4:07.61) after initial third-place finisher Rababe Arafi of Morocco was disqualified for stepping inside the kerb.
Aregawi was a the strong favourite going into the race in Poland and won by a comfortable margin of 6.51 seconds ahead of Sifuentes. The athlete's preparations for the race meeting in Sopot was overshadowed by media stories about her personal life regarding her marriage.
Swedish daily Expressen reported that Aregawi has been divorced from her husband Henok Weldegebriel since May 17th 2013. The couple had launched a firm defence of their relationship last year denying that it was a sham in order to secure citizenship.
"I don't know where these rumours come from. People are trying to make her feel bad. We have been married since 2008 and nobody paid to bring her to Sweden," husband Henok Weldegebriel said in an extensive interview with Dagens Nyheter in September 2013.
However, the report by Expressen revealed a document from the Swedish Tax Office (Skatteverket) that Aregawi's marital status was listed as divorced and had been so since May 17th last year.
Aregawi maintained to Aftonbladet, following the article in Expressen, that she and Henok are still married.
After her win Aregawi was quizzed by journalists if the media reports had affected her preparations.
"I don't want to talk about my private life here even though there was some talk. My focus was on my work and on my results so I don't really care to discuss my private life," Aregawi said via an interpreter.
Aregawi is regarded as one of the world's best runners in her field and won a gold medal at the Moscow World Championships in 2013. Her won on that occasion was also overshadowed as he refused to take part in the rainbow protest due to her religious beliefs.
She became a Swedish citizen in 2012 and is currently studying the language. Aregawi told Dagens Nyheter in September 2013 that she was keen to set the record straight after she was criticized for not participating in the rainbow protest.
"I respect all people and that all of us are equal. Sweden is a free country where everyone has the right to do what they want," she said.