2004–2010: Established actress
Blethyn co-starred as Bobby Darin's mother Polly Cassotto in Beyond the Sea, a 2004 biographical film about the singer. The film was a financial disappointment: budgeted at an estimated US$25 million, it opened to little notice and grossed only $6 million in its North American theatrical run. Margaret Pomeranz of At the Movies said that her casting was "a bit mystifying". Afterwards, Blethyn starred in A Way of Life, playing a bossy and censorious mother-in-law of a struggling young woman, played by Stephanie James, and in the television film Belonging, starring as a middle-aged childless woman who is left to look after the elderly relatives of her husband and to make a new life for herself after he leaves her for a younger woman. Blethyn received a Golden FIPA Award and a BAFTA nomination for the latter role. That same year she made her Broadway debut in the play 'Night Mother opposite Edie Falco. Ben Brantley of The New York Times wrote that while "she has the requisite fretful voice and fidgety mannerisms down pat, it's as if she is doing a technically perfect impersonation in a vacuum."
In early 2005, Blethyn appeared in the indie-drama On a Clear Day playing Joan, a Glasgow housewife, who secretly enrolls in bus-driving classes after her husband's dismissal. Her performance in the film received positive reviews; ABC writer MaryAnn Johanson wrote: "It's Blethyn, who wraps the movie in a cosy, comfortable, maternal hug that reassures you that it will weather its risk-taking with aplomb [...]." The film became a minor success at the international box-office chart, barely grossing $1million worldwide, but was awarded a BAFTA Scotland Award for Best Film and Screenplay.
A major hit for Blethyn came with Joe Wright's Pride & Prejudice, a 2005 adaptation of the same-titled novel by Jane Austen. Starring alongside Keira Knightley and Donald Sutherland, Blethyn played Mrs. Bennet, a fluttery mother of five sisters who desperately schemes to marry her daughters off to men of means. During promotion of the film, she noted of her portrayal of the character: "I've always thought she had a real problem and shouldn't be made fun of. She's pushy with a reason. As soon as Mr. Bennet dies, all the money goes down the male line; she has to save her daughters from penury." With both a worldwide gross of over US$121million and several Academy Award and Golden Globe nominations, the film became a critical and commercial success, spawning Blethyn another BAFTA Award nomination for Best Actress in a Supporting Role. In 2007, she appeared in the independent Australian coming-of-age comedy Clubland. Playing a character that was created specifically with her in mind, Blethyn portrayed a bawdy comedian with a sinking career faced with the romantic life of her young son, played by Khan Chittenden. The film was released in Australia in June 2007 and was screened Sundance Film Festival where distributed Warner Independent Pictures for a $4million deal and gained positive reviews. Los Angeles Times film critic Carina Chocano wrote, "the movie belongs to Blethyn, who takes a difficult, easily misunderstood role and gracefully cracks it open to reveal what's inside." The role earned her nominations for the Australian Film Institute Award and an Inside Film Award.
Also in 2007, Blethyn reunited with Joe Wright on Atonement, an adaptation from Ian McEwan's critically acclaimed novel of the same name. On her role of a housekeeper in a cast that also features Keira Knightley, Saoirse Ronan and James McAvoy, Blethyn commented: "It's a tiny, tiny part. If you blink you'll miss me." The film garnered generally positive reviews from film critics and received a Best Picture nomination at the 2008 Academy Awards. A box office success around the globe, it went on to gross a total of $129million worldwide. Blethyn also appeared as Márja Dmitrijewna Achrosímowa in a supporting role in the internationally produced 2007 miniseries War and Peace by RAI, filmed in Russia and Lithuania.
In 2008, Blethyn made her American small screen debut with a guest role on CBS sitcom The New Adventures of Old Christine, playing the neurotic mother to Julia Louis-Dreyfus' character in the fourth season episode "Guess Who's Not Coming to Dinner." The same year, she appeared in a single season ten episode of the NBC legal drama series Law & Order: Special Victims Unit. Her performance of a sympathetic fugitive of domestic violence and rape that killed her first husband in self-defense earned Blethyn another Primetime Emmy Award for Outstanding Guest Actress – Drama Series nomination. Blethyn provided the voice of Mama Heffalump in the animated Disney movie, Pooh's Heffalump Movie (2005) and later again provided the voice of Mama Heffalump in the Disney direct-to-video animated sequel Tigger & Pooh and a Musical Too (2009).
Blethyn's first film in two years, Rachid Bouchareb's London River opened at the 59th Berlin International Film Festival in 2009 where it won a Special Mention by the Ecumenical Jury. In the film, for which Blethyn had to learn French, she portrays a mother waiting for news of her missing child after the London bombings of July 2005, striking up a friendship with a Muslim man, whose child has also disappeared. Blethyn, who had initially felt sceptical and reticent about the film due to its background, was originally not available for filming but Bouchareb decided to delay filming to work with her. Upon release, the film received favourable reviews, particularly for its "dynamite acting". Mike Scott from The Times-Picayune commented "that Blethyn's performance is nuanced [...] it's that performance—at turns sweet, funny and heartbreaking—that ultimately draws viewers in and defies them to stop watching".
Also in 2009, Blethyn played a Benedictine nun in Jan Dunn's film The Calling, also starring Joanna Scanlan and Pauline McLynn. Dunn's third feature film, it tells the story of Joanna, played by Emily Beecham, who after graduating from university, goes against her family and friends when she decides to join a closed order of nuns. Released to film festivals in 2009, the independent drama was not released to UK cinemas until 2010. Critics compared it to soap opera and described it as "half Doubt, half Hollyoaks". Blethyn earned positive reviews for her performance; The Guardian writer Catherine Shoard wrote that "only she, really, manages to ride the rollercoaster jumps in plot and tone." Her last film of 2009 was Alex De Rakoff's crime film Dead Man Running alongside Tamer Hassan, Danny Dyer, and 50 Cent, in which she portrayed the wheelchair-using mother of a criminal who is taken hostage. The film received universally negative reviews from film critics, who deemed it to be full of "poor performances, stiff dialogue, [and] flat characters".
