Born in Oulunsalo, Finland, Aalto grew up in a musical family and received piano lessons from pianist and pedagogue Olga Maslak, born in Odessa, Soviet Union. Aalto wrote her first song at the age of five. Her close relatives include painter and documentary director Eeli Aalto and magician Simo Aalto. In 1998 at age 11, she won the Kotka Maritime Festival song contest for children with one of her own compositions. Aalto also won the Charlotte Church international singing competition, organised in US, in 2003 with her own composition. Aalto represented Finland in the Golden Stag International Song Contest in Romania in 2004. She went to the Madetoja secondary school for music, where she graduated in 2005. After graduation, she moved to Helsinki to study music at the Sibelius Academy, and at the same time also studied singing in the Helsinki Pop & Jazz Conservatory.

In 2007, she participated in Talent Suomi (“Talent Finland”), finishing in the top three.

Aalto took part on two separate occasions in the selection process in a bid to represent Finland in the Eurovision Song Contest. She participated in the qualifying rounds in Finland for Eurovision 2011, placing second to Paradise Oskar who went on to represent Finland. She received 40.7% of the public televotes, compared to 46.7% for Oskar. Aalto’s recording was released as a single by Yume Records, a self-release record label she founded together with Teemu Roivainen in 2011.

Following her performance of “Blessed with Love” for qualification in Eurovision 2011, that December she was involved in the Santa Claus Season’s Greetings Song Contest, where she sang “Ai De Zhu Fu,” a Chinese (Mandarin) version of her Eurovision song “Blessed with Love”.

In November 2012, Aalto was guest vocalist at Robert Wells’s highly successful show Rhapsody in Rock at Shanghai Daning theatre. Following a successful performance in Shanghai in May 2013, opening for Spanish tenor José Carreras and singing several songs in Chinese, Aalto returned to the city to duet with tenor Han Peng at the Closing Ceremony of the Shanghai International Film Festival in June 2013, broadcast to over 800 million viewers in 10 countries.

Aalto participated in season one of The Voice of Finland. In the blind auditions, broadcast on 6 February 2012 on the Finnish commercial television channel Nelonen, she performed “Taking Chances” from Celine Dion with all four coaches, Elastinen, Lauri Tähkä, Paula Koivuniemi and Michael Monroe turning their chairs. She opted to be part of Team Monroe.

Finding great reception from Chinese audiences, in July 2013 Aalto went on to release a full album destined for Mainland China and other Chinese markets also titled Ai De Zhu Fu. On the album she performed nine of the album’s 13 tracks in Mandarin language.

Aalto had a nine-year relationship with singer Teemu Roivainen, but the couple broke up in 2013. Aalto and Roivainen continued collaborating in music. Aalto later began a relationship with a female fan, Meri Sopanen, who worked as a personal trainer and life coach. They became engaged on their two-year anniversary in August 2016. Aalto now identifies as a lesbian. Aalto and Sopanen moved to London in January 2017. They got married in April 2020 and Meri took Saara’s last name.

Aalto auditioned for the thirteenth UK series of The X Factor in 2016 in front of attending judges Simon Cowell, Louis Walsh and Nicole Scherzinger, singing a cover of Sia’s “Chandelier”, which earned her three yeses from the judges. At bootcamp, she performed “On the Radio” by Donna Summer and was sent through as part of the over-25s category, mentored by Sharon Osbourne, who was not present at her audition. At the six-chair challenge, she performed “I See Fire” by Ed Sheeran and was sent home by Osbourne who stated a lack of connection. However, after the crowd chanted to bring her back, Aalto was given a second chance and performed “Je suis malade” by Serge Lama, which caused the crowd to turn on her, while Scherzinger criticized her song choice, stating “we ain’t in France”. Osbourne then asked Aalto to leave.

In a press-conference in December 2016, Aalto revealed that she works with the joint effort of ROAR Global and Global career management companies, and that she has signed a five-album recording deal with Sony Music UK and Sony Music Finland. In October 2017, Aalto announced she had left Sony Music for Warner Music Group. In a statement, she said: “I was honoured I was signed to Sony. But later I felt like they weren’t the right team. When I met the people at Warner they were very excited about my style and making me into this big theatrical artist.” On 7 November 2017, it was announced that Aalto would represent Finland in the Eurovision Song Contest 2018 in Lisbon, Portugal. The three bidding entries were released by Yle and Saara Aalto, along with an accompanying music video. Aalto was a judge on the second series of the Finnish version of The X Factor, mentoring the girls. Aalto could not attend the finale night of The X Factor Finland due to her commitments with Eurovision, so Terry represented her instead, but her category’s last girl, Tika Liljegren, was crowned the winner, making Aalto the winning mentor. Aalto announced in March 2018 via social media that her first album under Warner Music Group, Wild Wild Wonderland, would be released on 27 April 2018.

In 2019 Aalto participated in the eleventh series of Dancing on Ice. She was partnered with Hamish Gaman, and after reaching the final, she and Garman finished in third place.. Aalto’s song Dance Like Nobody’s Watching was the official song of Pride in London 2019. That same year, Aalto founded her own record label titled No Fear Music. It was under that label she released her Fairytale – International EP.

In September 2020, Aalto announced the release of her single, “When the Sun Goes Down”, a collaboration with British drag queen Baga Chipz. She was also revealed to have parted ways with Warner Music in Spring 2020.