Platten was born on May 20, 1981, in New York City to a mother of Irish ancestry, and grew up in Newton Centre, Massachusetts and attended the Mason-Rice Elementary School. She was raised Jewish. Platten studied classical piano from the age of 5 and then took up guitar in high school. She attended Buckingham Browne and Nichols high school, where she sang in the school's singing group. At Trinity College, she was a member of the Trinity College Trinitones, the college's first all-female a cappella group.

As a part of a study abroad program, she went to Trinidad to do an internship at a diplomat's office and at a record label. While she was there, she sang backup for a friend's band in front of over 80,000 people at the International Soca Monarch finals in 2002. According to Platten, from that moment on she knew she had to pursue music full-time.

Platten graduated from Trinity College with a degree in international relations in 2003. She then moved to New York City's Greenwich Village performing in a Prince and Sly and the Family Stone cover band called Dayz of Wild. She performed her solo music around the Village and eventually began touring the country.

In 2012, Platten married Kevin Lazan in a Jewish ceremony.

Platten released her debut studio album Trust in Me in 2003, which she has called "a collection of demos". Her second album, Be Here, was released from Rock Ridge Music in 2011. Her 2011 single "1,000 Ships" peaked at number 24 on the US Billboard Adult Top 40 chart, also playing at various radio stations. An earlier song, "Seven Weeks", was used for the film The Good Guy. The theme song for ABC Family's Jane by Design, "Work of Art" was performed by Platten on hire. Her song "Begin Again" was used in the hit ABC Family TV show Pretty Little Liars 100th episode "Miss Me x 100". Her song "Don't Care What Time It Is" was used in VH1's Basketball Wives. Her song "You're Safe" was used in MTV's Finding Carter in September 2014. On June 27, 2014, Platten debuted "Fight Song" on the music social network We Heart It as part of an Artist spotlight.

On September 11, 2015, Platten released second single named "Stand by You" from Wildfire. It has peaked in the top ten on charts in Canada and the United States, and has peaked in the top twenty on charts in Australia and Poland. The song has since been certified Platinum in the United States.

On New Year's Eve 2016, Platten co-headlined the Times Square Ball festivities in New York City's Times Square alongside Gavin DeGraw, where she performed "Fight Song", "Stand by You", "Beating Me Up", and John Lennon's "Imagine".

"Broken Glass", the lead single from her fourth studio album, Waves, was released on August 18, 2017. The album was released on October 27, 2017.

On April 14, 2018, Platten forgot the lyrics to the Star Spangled Banner while singing the national anthem at the inaugural game of the Utah Royals Football Club. She apologized both after completing the song and at her post-game concert.