[3][4] Her parents divorced when she was five, and Sossamon and her sister were then raised by her mother, who married Randy Goldman, a salesman and manager of an auto dealership.

[8] Around that time, Sossamon established her early career by modeling for various companies including Sassy Magazine, Unionbay Clothing, American Eagle Outfitters, and Planned Parenthood.

In 1997, Sossamon guest-starred as several characters in three episodes of Mr. Show with Bob and David, and two years later, she was discovered by casting director Francine Maisler, while assisting a fellow DJ at Gwyneth Paltrow's brother's birthday party.

[8] Sossamon beat Kate Hudson for the lead female role in Brian Helgeland's adventure dramedy A Knight's Tale, opposite Heath Ledger.

The film premiered on May 11, 2001,[10] and received average reviews,[11] with her part getting an equally mixed response; Robin Clifford for Reeling Reviews concluded that Sossamon was "pretty but little more than an object of affection"[12] and Rob Blackwelder of SPLICEDwire called her role "the movie's weakest link", noting that although Sossamon was a "wonderfully wicked flirt", her character "isn't terribly well established and she's the most jarringly modern sight in this ancient tale".

In 2002, Sossamon starred in the romantic comedy 40 Days and 40 Nights, as Erica Sutton, the love interest of Josh Hartnett's character, Matt Sullivan.

It received mixed reviews from critics, but was a major box office success, earning a worldwide total of US$95,146,283 on a production budget of US$17 million.

[22] David Noh of Film Journal International found her performance "heartbreaking" and described it as "an uncanny blend of fragile-fey and urchin-tough, marked by a feverish wit which often proves her undoing as much as her salvation".

It was released in late 2003, to extremely poor reviews;[27] Critical reception for Sossamon was average with 7M Pictures finding the movie "well acted" by the leads but eFilmCritic.com remarking that she, "so charming in both "A Knight's Tale and 40 Days and 40 Nights, is given very little to do besides utilize her 'tortured soul with dark eye makeup' schtick".

[8] She has recalled seeing her acting career in a "total stop" after giving birth, but nevertheless described her absence on screen as a "blessing in disguise for many reasons".

[31] Her only acting appearance of 2004 was a guest-starring role on the NBC series Law & Order: Special Victims Unit, in the episode “Doubt”.

[32][33] Her next vehicle was the horror thriller Devour, in which she played Marisol, one of several friends who become increasingly addicted to a video game that has an evil agenda.

Critical reception towards the picture was unanimously negative,[34] but a few reviewers showed approval of the cast members' performances, with DVD Talk noting that Sossamon, alongside co-star Dominique Swain, "do the best they can with the material they're given, but end up as not much more than eye-candy stuck in a sea of aimless gore and maddeningly vague plot droppings".

Distributed for a limited release to certain parts of the United States only, the movie premiered on August 26, 2005,[citation needed] to lackluster sales and critical failure.

Sossamon starred as Beth Raymond in One Missed Call, a remake of Takashi Miike's 2003 Japanese horror film of the same name.

The movie had its U.S. premiere on January 4, 2008,[58] and fared "decently" on its opening weekend, with an estimated US$13.5 million in sales, as noted by Box Office Mojo.

[61] Georgia Straight writer Steve Newton felt that Sossamon tried "desperately to bring some substance to her role", but the "preposterous script" made it a "lost cause".

[citation needed] She played Concetta, a woman faced with the challenges of raising her sick child and supporting her husband in the indie drama Life Is Hot in Cracktown, directed by Buddy Giovinazzo, and co-starring Kerry Washington, Lara Flynn Boyle and Brandon Routh.

The movie was first screened at the 2009 Fantasia International Film Festival,[63] and received a limited theatrical release in June that year; it went to DVD two months later.

[68] During an interview with Keba Robinson, of Hook and Line magazine, Sossamon explained that her initiative for creating Maudegone was about having "some sort of control and do creative things and feel like it was something that I started.

[75] Meanwhile, Colin Convert for Star Tribune wrote in his review: "The key to the movie is casting the right femme fatale, and non-actress Shannyn Sossamon, the mystery woman's eerie doppelgänger, wins the part and her director's heart".

[76] She was cast with Ashley Bell, Dominic Monaghan and Shawn Ashmore in the indie thriller The Day,[77] which follows a group of people fighting to stay alive in a post-apocalyptic future.

It received generally mixed or average reviews;[78] while The Los Angeles Times and The New York Daily News praised the cast,[79][80] Blu-ray.com and Paste magazine criticized Sossamon for "weaving in and out" of her character's southern accent.

Chicago Sun-Times critic Charlie Schmidlin concluded that the actress "radiates warmth" and noted that her part in the movie "is the most natural and welcome performance I've seen from her".

[88] The 13-minute video, directed by Adam Smith and co-starring Damian Lewis, is about a car delivery man who gets caught up in a dangerous chase involving a woman in trouble (who is played by Sossamon).

[93] At the time, it was announced that Sossamon was cast to play one of the main parts in M. Night Shyamalan's limited series for FOX, Wayward Pines.

[96][97] Wayward Pines received mostly favorable reviews from critics[98] and after a debut described as "soft" by Deadline Hollywood,[99] viewership for the series grew in subsequent episodes.

[100][101][102] She provided her voice for a character named Lorna during an episode of Over the Garden Wall, which aired on November 6, 2014 ("Chapter 7: The Ringing of the Bell") She next had a starring role in the supernatural horror sequel Sinister 2,[103] where she played a mother whose sons are tormented by ghostly children.