Katharine McPhee parlayed her early success as the runner-up on American Idol's fifth season into a long-running career. During the 2000s and 2010s, she not only balanced roles on TV series such as Smash and Scorpion with her music, but also demonstrated her range as a singer. Along with frequent collaborations with Idol contributors including Randy Jackson, Andrea Bocelli, and David Foster, McPhee's smooth style felt equally at home on pop albums like her self-titled 2007 debut and 2015's Hysteria, and on more traditional fare such as 2017's I Fall in Love Too Easily.
A native of Sherman Oaks, California, McPhee began singing at age two. Her mother, Patricia McPhee, is an established singer in her own right, performing and recording as Peisha McPhee. She helped Katharine develop as a vocalist and later, along with McPhee's older sister Adriana, served as a vocal coach on American Idol. Though McPhee sang and acted throughout her childhood and high-school years, she began taking singing more seriously in college, attending Boston Conservatory as a musical theater major. After three semesters, however, she left for Los Angeles to audition for film and television work. McPhee scored roles in the film Crazy, a musical about Hank Garland, and an MTV series, You Are Here, which didn't make it to the air. She also appeared in productions of Annie Get Your Gun and The Ghost and Mrs. Muir before auditioning for American Idol in 2005.
McPhee made the final 12, her performances of songs such as "Someone to Watch Over Me," "Come Rain or Come Shine," and "Black Horse and the Cherry Tree" made her one of the favorites of American Idol judges and viewers. In May 2006, she became the runner-up to the season 5 winner, Taylor Hicks. After the American Idol season ended, McPhee was signed by show creator Simon Fuller's 19 Recordings Limited label and released her first single, Somewhere Over the Rainbow/My Destiny; it reached number 12 on the Billboard Hot 100 and became the second best-selling single of 2006. A few months later, she joined the rest of the finalists and Hicks on the American Idols LIVE! tour and also toured with Andrea Bocelli, who appeared on American Idol as a guest judge. She also collaborated on a version of "Can't Help Falling in Love" that appeared on Bocelli's 2006 album Under the Desert Sky.
McPhee's self-titled debut album, which included collaborations with Nate "Danja" Hills, the Neptunes' Chad Hugo and songwriter Kara DioGuardi, arrived in January 2007; it debuted at number two on the Billboard 200 chart, while the single "Over It" was certified gold in 2008. In March 2008, she appeared on American Idol judge Randy Jackson's album Randy Jackson's Music Club, Vol.1, on which she duetted with fellow season five contestant Elliott Yamin on the song "Real Love." Later that year, she performed at a tribute concert for producer/songwriter/composer David Foster, another artist frequently involved with Idol. McPhee also made her studio acting debut with that year's The House Bunny. The following year, she appeared on an episode of CSI: NY. In January 2010, McPhee made her Verve Forecast debut with her second album Unbroken, which peaked at number 27 on the Billboard 200 chart. That October, she released the holiday album Christmas Is a Time...To Say I Love You, which debuted on the Billboard Top Holiday Albums Chart at number 11.
For the rest of the 2010s, McPhee balanced her acting and singing careers. In 2011, she landed a pivotal role on NBC's musical drama Smash, which ran for two seasons. She also appeared in the 2011 indie films You May Not Kiss the Bride and Peace, Love & Misunderstanding. In 2014, she began a four-year run on the CBS drama Scorpion, playing the role of Page Dineen until the series ended in 2018. During her time on the show, McPhee released Hysteria, her first pop album in five years, in 2015, and followed it with 2017's I Fall in Love Too Easily, a standards collection produced by Don Was. In 2018, she made her Broadway debut as Jenna in the musical Waitress. In May of that year, McPhee recorded the song "Living in the Moment," a song written by Carole Bayer Sager, Jay Landers, and Walter Afanasieff for the movie Book Club.