In 2001 she joined the Canadian teen drama television series Edgemont as recurring character Bekka Lawrence, later becoming a series regular on the show, which she remained through the end of the show’s run in 2005. She was also a series regular on another Canadian television series, YTV’s short-lived 2030 CE in 2002.

She guest starred in an episode of The L Word as Roxanne in 2004. She went on to appear as a series regular in the short-lived ABC teen drama series Life as We Know It as Sue; the series which ran for just one season. In 2006 she appeared in the film She’s the Man and co-starred in The Covenant. She was cast in another ABC television pilot, Secrets of a Small Town, though it was not picked up to series.

She was cast as Lisa in the film Amusement in 2006; the film was set to be released theatrically by New Line Cinema, but after a negative reaction it was released instead straight-to-DVD in 2009. The same year, Lucas was announced to have signed on as Riley Richmond, one of the lead roles in another CW television series Melrose Place, a followup to the popular 1990s series of the same name.

In 2007, she joined the cast of CSI: Crime Scene Investigation playing the recurring character of Ronnie Lake. Despite appearing in four episodes, rumours were denied that she would be a permanent replacement for Sara Sidle. The character was written out of the series with no explanation. She also appeared in a made-for-television film Split Decision.

In 2008, she guest starred as Kimberly MacIntyre in four episodes of The CW’s 90210. She also starred in a leading role as Lily in J. J. Abrams Cloverfield, which was a box office success and was well received by critics.

Lucas was part of the main cast of the NBC sitcom Friends with Benefits, which aired during the summer of 2011 before being cancelled. In 2011 she played Haley in Big Mommas: Like Father, Like Son, where she showcased her singing talents as well as her acting skills.

In 2012 Lucas was cast as the lead character, Skye Yarrow, in the CW series Cult, which was filmed in Spring 2012. In 2012 she was cast in a main role in the 2013 remake of the classic horror film The Evil Dead.

In 2014, Lucas appeared in Pompeii directed by Paul W. S. Anderson.

From 2015 to 2019, she has had a regular role in FOX’s Gotham as Tabitha Galavan.

In April 2017, Lucas announced her engagement to chef Alex Jermasek.