Lia Cirio began her training at Swarthmore Ballet Theatre with Lori Ardis. She went on to train at the Central Pennsylvania Youth Ballet under the direction of Marcia Dale Weary and Darla Hoover, where she also studied privately with Theresa Crawford and Rafael Grigorian.

From 2008-2009, Cirio toured with Trey McIntyre Project, performing throughout the United States and the world. She danced principal roles in McIntyre's Reassuring Effects of Form, Poetry, and A Day in the Life, and originated roles in various new works by McIntyre.

Her repertory with Boston Ballet includes featured and/or principal roles in classics such as Sir Frederick Ashton's Cinderella (Cinderella, Winter Fairy); George Balanchine's Coppélia, Jewels (Diamonds and Emeralds), Symphony in C (second movement), Symphony in Three Movements, Theme and Variations, Apollo, Divertimento No.15, Episodes, Who Cares?, Concerto Barocco, The Four Temperaments, Ballo de la Regina, La Valse, Serenade,  A Midsummer Night's Dream, and Kammermusik No. 2; Val Caniparoli's Lady of the Camellias (Olympe); Florence Clerc's La Bayadère (Nikiya, Gamzatti, Lead Shade) and Les Sylphides (the Sylph); Sorella Englund's La Sylphide (principal); Maina Gielgud's Giselle (Myrtha, Peasant pas de deux); Harald Lander's Études (the Ballerina); Vaslav Nijinsky's Afternoon of the Faun (principal nymph); Mikko Nissinen's Swan Lake (Odette/Odile, pas de trois, pas de cinq, Four Little Swans) and The Nutcracker (Sugar Plum Fairy, Dew Drop Fairy, Snow Queen, Arabian); Rudolf Nureyev's Don Quixote (Kitri, Mercedes, Queen of the Dryads); and Marius Petipa's The Sleeping Beauty (Aurora,  Lilac Fairy, Woodland Glade Fairy) and Paquita (principal role),  along with numerous pas de deux. She has danced principal roles in Peter Martins' Barber Violin Concerto; John Neumeier’s Third Symphony of Gustav Mahler; and Jerome Robbins' Antique Epigraphs.

Her contemporary repertoire includes works by Christopher Bruce, Val Caniparoli, Jeffrey Cirio, Alexander Ekman, Jorma Elo, Jiří Kylián, William Forsythe, Wayne McGregor, Mark Morris, Heather Myers, Helen Pickett, Twyla Tharp, Christopher Wheeldon, Lila York, and Petr Zuska. She originated roles in Elo's Carmen (Micaela), Brake the Eyes, Sharper Side of Dark, and Awake Only.

At age 16, she was awarded a Level One award from the National Foundation for Advancement of the Arts and was a Presidential Scholar in the Arts finalist. She was also awarded the top scholarship and Founders' Award presented by Barbara Weisberger at the Regional Dance America Festival. She was Boston Ballet’s Princess Grace Nominee in 2004. Cirio was named in Dance Magazine's first "On the Rise" feature article, and has been featured in additional articles in Dance Magazine, Dance Spirit, and on the cover of Pointe. She has been hailed as "one of the most accomplished actress-dancers in the company" by The Patriot Ledger, and as "an outstanding performer with tremendous stage presence" during Boston Ballet's Spain tour. She has performed in galas around the world, most recently with United Ballet Company. Cirio is currently pursuing a degree in Public Relations at Northeastern University. She also serves as Assistant to the Artistic Director, as well as a dancer with Cirio Collective. She is the sister of American Ballet Theatre Principal Dancer and former Boston Ballet Principal Dancer Jeffrey Cirio. In 2018, Cirio made her choreographic debut with Sta(i)r(e)s during BB@home: ChoreograpHER and in 2019, she choreographed the peppermint wind for Boston Ballet School’s Next Generation.

At 16, Cirio was invited by Mikko Nissinen to join Boston Ballet II. She was promoted to Boston Ballet's corps de ballet in 2004, to second soloist in 2006, and to soloist in 2007. Following her time with Trey McIntyre Project, she returned to Boston Ballet for the 2009-2010 season and was named principal dancer in 2010.