She won the AACTA Award for Best Guest or Supporting Actress in a Television Drama for the 2015 miniseries Peter Allen: Not the Boy Next Door.

Back in Brisbane she attended Twelfth Night Theatre Junior Workshop and in 1970, during the Captain Cook Bicentenary Celebrations, Thornton appeared before Queen Elizabeth II as Rosa Campbell-Praed in Looking Glass on Yesterday.

[4] 1986 saw her in The Lighthorsemen, the TV adaptation of Nevil Shute's novel The Far Country,[5] Great Expectations: The Untold Story and Slate, Wyn & Me.

She starred as Laura Joy Gibson in the Australian television series SeaChange from 1998 to 2000,[6] winning the Most Outstanding Actress award in 1999 and 2000.

Thornton's stage performances include a 2002/03 touring production of The Blue Room directed by Simon Phillips for the Melbourne Theatre Company opposite Marcus Graham.

[7] In 2009 she made her debut with Opera Australia in its production at Melbourne's Arts Centre as Desiree Armfeldt in Sondheim and Wheeler's A Little Night Music, directed by Stuart Maunder.

[8] In 2014, she won critical acclaim for her portrayal of Blanche DuBois in Tennessee Williams' play A Streetcar Named Desire for the Black Swan State Theatre Company in Perth.

[12] In 2002, Thornton starred in Australian thriller The Pact, directed by Strathford Hamilton, written by Hugh O'Brien.

In 2010, she appeared in Underbelly: The Golden Mile as recurring character Geraldine "Gerry" Lloyd, an Australian Federal Police detective and investigator for the Wood Royal Commission.

[15] In 2016, Thornton appeared in the fourth season of SoHo drama series Wentworth for seven episodes as a special guest star.

She portrayed the character of Sonia Stevens (initially played by Tina Bursill in Prisoner), a woman on remand for the suspected murder of her best friend.

[19] More broadly he referred to changing Australian cultural values which were well reflected in the types of places in which Sigrid Thornton had acted: the Riverland during the 1980s All the Rivers Run and the coast in the 2000s SeaChange.