Mälkki was born in Helsinki on March 13, 1969. She studied several instruments as a child but was given a cello at school, brought it home, and announced that she wanted to play it. She settled on a musical career after attending a music festival in her teens and took cello lessons with Hannu Kiiski. While living in Stockholm, Sweden, and studying cello, her school invited famed conductor Esa-Pekka Salonen to give a conducting lesson. Mälkki prepared a piece and felt an instant connection with the activity. She continued to play the cello, even winning a place as principal cellist of the Gothenburg Symphony, but she commuted between Gothenburg and Helsinki so that she could take conducting lessons with Jorma Panula, Leif Segerstam, and Eri Klas. In 1998, she participated in a conducting workshop at Carnegie Hall with Salonen and Panula.
Between 2002 and 2005, Mälkki served as the artistic director of the Stavanger Symphony Orchestra in Norway. She made her debut with the Ensemble InterContemporain in Paris in 2004 and was named music director two years later, becoming the first woman to hold the post and remaining until 2013. During this period, she made guest conducting appearances with the New Zealand Symphony, the Saint Louis Symphony, the London Sinfonietta (which she led at the BBC Proms in 2007), and the Los Angeles Philharmonic. With that group, she made her debut in 2010 and became the principal guest conductor in 2017 as the first woman to hold the post. Mälkki also served as the principal guest conductor of the Gulbenkian Orchestra in Lisbon from 2013 to 2016. In the autumn of 2016, she was named the chief conductor of the Helsinki Philharmonic, once again become the first woman to hold the post. Her contract was subsequently extended until 2023. Mälkki has also conducted opera, becoming the first female conductor at La Scala in Italy, and making her debut at the Metropolitan Opera in a production of Kaija Saariaho's L'amour de loin.
Mälkki has led a variety of orchestras in recordings on Kairos, BIS, Alba, and other labels, mostly in contemporary works. In 2020, she appeared with conductor Gerd Albrecht and the ORF Vienna Radio Symphony Orchestra on an album of works by Alexander Zemlinsky. ~ James Manheim, Rovi