In March 2014, she and Mima Ito won their first doubles title at ITTF World Tour German Open. They became the youngest ever winners of the doubles competition in the ITTF World Tour. She was part of the Japanese team in 2014 Asian Games, but lost to China in the final.

In April 2014 she won her second doubles title with Mima Ito at the ITTF World Tour Spanish open.

In December 2014, she won the doubles title with Mima Ito at the ITTF World Tour Grand Finals in Bangkok. The pair defeated Singapore pair of Feng Tianwei and Yu Mengyu in the semi-finals and Poland pair of Katarzyna Grzybowska and Natalia Partyka in the final.

On 5 July 2015, Miu Hirano and Mima Ito won the Women’s Doubles title at the ITTF World Tour Korean Open. This was their third doubles title since 2014.

In April 2016, she won her first women’s singles title in ITTF World Tour Polish Open by defeating Yu Mengyu in the Final.

On 9 October 2016, with the absence of Chinese players, she seized the opportunity to win the Women’s World Cup in Philadelphia, USA after defeating Mima Ito in the quarterfinals, Feng Tianwei in the semi-final and Cheng I-ching in the final. This marks the youngest women’s World Cup Champion and the first non-Chinese player to win the title.

On 22 January 2017, she won All Japan Championships by defeating Kasumi Ishikawa 4–2 in the final at the Tokyo Metropolitan Gymnasium. On 14 April 2017, she defeated the world ranked No.1 player Ding Ning at the 2017 ITTF Asian Table Tennis Championships. The following day of the tournament, she defeated the world ranked No.2 player Zhu Yuling in the Semifinals and Chen Meng world ranked No.5 in the Finals, where she set a new record for the youngest winner of the Asian Championships in the Singles Event. She became the third non-Chinese player ever and the first non-Chinese player since Chire Koyama in 1996 to win the Singles title.

In the 2017 World Table Tennis Championships in Düsseldorf, Hirano progressed to the singles semi-finals but lost to Ding Ning of China. She obtained a joint bronze medal with Liu Shiwen of China. This ended a long medal drought for Japan in women’s singles at the world championships since Toshiko Kowada achieved the gold medal in 1969 World Championships.