Sunrise Coigney

Ruffalo had minor roles in films like The Dentist (1996), the low-key crime comedy Safe Men (1998) and Ang Lee's Civil War Western Ride with the Devil (1999). Through a chance meeting with Writer Kenneth Lonergan, he began collaborating with Lonergan and appeared in several of his plays, including the original cast of This is Our Youth (1996), which led to Ruffalo's role as Laura Linney's character's brother in Lonergan's Academy Award-nominated 2000 film You Can Count On Me. He received favorable reviews for his performance in this film, often earning comparisons to the young Marlon Brando, and won awards from the Los Angeles Film Critics Association and Montreal World Film Festival.

Since June 2000, Ruffalo has been married to Sunrise Coigney and they have three children: son Keen (b. 2001), and daughters Bella Noche (b. 2005) and Odette (b. 2007). They live in Manhattan.

This led to other significant roles, including the films XX/XY (2002), Isabel Coixet's My Life Without Me (2003), Jane Campion's In the Cut (2003), Michel Gondry's Eternal Sunshine of the Spotless Mind (2004), and We Don't Live Here Anymore (2004), which is based on two short stories written by Andre Dubus. He appeared opposite Tom Cruise as a narcotics detective in Michael Mann's crime thriller Collateral (2004).

Ruffalo has given interviews to We Are Change, a 9/11 'truth' group, in both 2007 and 2011. Ruffalo stated: "I'm baffled by the way all three buildings came down. My first reaction was that buildings don't fall down like that. I've done quite a bit of my own research ...The fact that the 9/11 investigation went from the moment the planes hit to the moment the buildings fell, and nothing before or after, I think, makes that investigation completely illegitimate. If you're going to do a Criminal investigation, you have to find a motive. We didn't follow that. It was quickly pushed away, obviously. There was no evidence at the biggest crime scene. None of us know what happened but I'm totally and completely behind reopening that investigation. Where is the money? Follow the money, guys!"

On December 1, 2008, Ruffalo's brother, Scott, was shot in the head at his Beverly Hills condominium, and died a week later. The case remains unsolved.

In 2008, Ruffalo expressed concern that gas companies were eyeing his family's land in Callicoon, New York. After doing his own investigation, New York magazine wrote, he becomes "anti-fracking's first famous face." On October 4, 2010, Ruffalo appeared on The Rachel Maddow Show to discuss hydraulic fracturing and the FRAC Act of 2009. He claimed in the December 2010 issue of GQ magazine that after he organized screenings in Pennsylvania of a documentary about natural-gas-drilling called Gasland, he was placed on a terror advisory list. The Department of Homeland Security denied the claim.

In 2011, he added: "The Commission didn't really do anything about before the buildings were struck or afterward. There just seems to be more questions left unanswered than anything else. I don't want to jump to any conclusions but I don't think it's ever been given its due diligence, considering that it's the largest crime ever committed on US soil. Building Seven – a lot of people don't even know about that ... The world has changed because of it and not in a good way. We've been militarized and lost many of our civil liberties. More people die from smoking cigarettes each year and we give this a lot more play than that."

Ruffalo starred in The Avengers (2012), the sixth installment of the Marvel Cinematic Universe, replacing Edward Norton as Dr. Bruce Banner / Hulk. Ruffalo received critical acclaim for his performance and is under contract to reprise the role in any Future film appearances of the character produced by Marvel Studios. Ruffalo also made a cameo appearance as Banner in Iron Man 3, making him the first actor to reprise the character in a live-action film. He reprised the role again in Avengers: Age of Ultron (2015) and Thor: Ragnarok (2017), and will do so once more in the upcoming films Avengers: Infinity War and its untitled sequel set for release in 2018 and 2019, respectively.

The Solutions Project is an organization founded by engineering professor Mark Z. Jacobson (Stanford University), Marco Krapels, documentary filmmaker/activist Josh Fox and Mark Ruffalo, with the aim of moving The United States towards 100% renewable Energy, including the use of wind power and solar power. The organization says this Energy transition is mainly social and political in nature, not technical. In 2014, Ruffalo spoke out against Israel's Operation Protective Edge, Israel's 7-week war against Hamas, tweeting: "Israel destroys el-Wafa hospital as staff evacuates all patients". After receiving criticism for defending Palestinians, Ruffalo responded: "Sorry, I thought blowing up Hospitals was something that all human beings could agree was off limits." Finally, in response to accusations of anti-Semitism, Ruffalo responded, citing a Tikkun Daily article: "Empathizing w/ Gaza does NOT make me anti-Semitic, nor pro-Hamas or anti-Israel. It makes me human."

In 2015, Ruffalo received his second Academy Award nomination for his portrayal of Wrestler Dave Schultz in the biographical drama Foxcatcher. Later in the year, he starred as a bipolar father-of-two in the independent comedy film Infinitely Polar Bear, for which he earned a Golden Globe Award nomination, and he also appeared as Journalist Michael Rezendes in the drama film Spotlight, for which he earned his third Academy Award nomination and a BAFTA Award nomination.

Ruffalo has a house in Sullivan County, New York and in 2016 described the Catskill Mountains as his home.

In June 2017, Ruffalo endorsed Labour Party leader Jeremy Corbyn in the 2017 UK general election. He tweeted: "Because @jeremycorbyn offers people an alternative to the Corporate status quo, which never ends well for them, I humbly endorse Corbyn."