In 1961 he moved back to Wichita to join his father’s business, Rock Island Oil & Refining Company (now known as Koch Industries). In 1967, he became president of the business, which was then a medium-sized oil firm. In the same year, he renamed the firm Koch Industries in honor of his father. Charles’s brothers Frederick and Bill had inherited stock in Koch Industries. In June 1983, after a legal and boardroom battle, the stakes of Frederick and Bill were bought out for $1.1 billion and Charles and his younger brother David became majority owners in the company. Despite the settlement, legal disputes continued until May 2001, when CBS News reported that Koch Industries settled for $25 million.

In 1977 he co-founded the Cato Institute with Edward H. Crane and Murray Rothbard.

Koch supported his brother’s candidacy for vice president on the Libertarian Party ticket in 1980. After the bid, Koch told a reporter that conventional politics “tends to be a nasty, corrupting business … I’m interested in advancing libertarian ideas”. In addition to funding think tanks, Charles and David also support libertarian academics and Koch funds the Charles G. Koch Summer Fellow Program through the Institute for Humane Studies which recruits and mentors young libertarians. Koch also organizes twice yearly meetings of Republican donors.

In 2002, Koch Industries donated $6 million to renovate the Wichita State University basketball arena. The gift was given in honor of Koch, and the arena was subsequently renamed the Charles Koch Arena. Koch has continued to be a major donor to both the university and its athletic program. In December 2014, Koch Industries and the Koch family foundation donated $11.25 million to the university, the largest one-time gift in school history, with $4.5 million of that going toward a plan to renovate the arena and expand the athletic program’s academic support center. Several months later, when men’s basketball head coach Gregg Marshall was considering an offer to become head coach at the University of Alabama, Koch led a group of local business leaders and WSU boosters that raised Marshall’s annual salary from $1.85 million to $3 million and kept him at the school. The raise was seen as an unprecedented move for a school outside the Power Five conferences, and likely to make Marshall among the 10 highest-paid college basketball coaches.

In 2006, Koch Industries generated $90 billion in revenue, a growth of 2000 times over, which represents an annual compounded return of 18%. As of 2014, Koch was worth approximately $41.3 billion (in 2013 $36 billion) according to the Forbes 400 list. Koch would routinely work 12-hour days at the office (and then spent more time working at home), weekends, and expected executives at Koch Industries to work weekends as well.

Koch’s business philosophy, “market-based management” (MBM), is described in his 2007 book The Science of Success. In an interview with the Wichita Eagle, he said that he was motivated to write the book by Koch Industries’ 2004 acquisition of Invista so he could give new employees a “comprehensive picture” of MBM. According to the website of the Market-Based Management Institute, which Koch founded in 2005, MBM is “based on rules of just conduct, economic thinking, and sound mental models”, harnessing the dispersed knowledge of employees just as markets harness knowledge in society. “It is organized in and interpreted through five dimensions: vision, virtue and talents, decision rights, incentives, and knowledge processes.” In the book, Koch attempts to apply Friedrich Hayek’s spontaneous order theory and Austrian entrepreneurial theory, such as that of Mises and Israel Kirzner, to organizational management.

In 2008, Koch was included in Businessweek’s list of top 50 American givers. Between 2004 and 2008, Koch gave $246 million, focusing on “libertarian causes, giving money for academic and public policy research and social welfare.” Koch was awarded an Honorary Doctorate from George Mason University in recognition of his financial support “through scholarships, faculty recruitment, and research grants”.

In 2011, Koch was awarded the William E. Simon Prize for Philanthropic Leadership. The award honors “the ideals and principles which guided William E. Simon’s giving, including personal responsibility, resourcefulness, volunteerism, scholarship, individual freedom, faith in God, and helping people to help themselves.”

Due to his business interests in fossil fuel industry, Koch has heavily funded organizations and politicians who deny or downplay climate change and oppose environmental regulations. A leaked 2012 fundraising plan indicated that the Charles G. Koch Charitable Foundation contributed $25,000 in 2011 to the Heartland Institute, an American conservative and libertarian public policy think tank. Koch has also supported the Berkeley Earth Surface Temperature project, a scientific effort to compile an open database of the Earth’s surface temperature records.

In July 2015 Charles Koch and his brother were praised by President Obama and Anthony Van Jones for their bipartisan efforts to reform the criminal justice system. For roughly a decade Koch has been advocating for several reforms within the prison system, including the reduction of recidivist criminals, easing the employment process for rehabilitated persons, and the defense of private property from asset forfeiture. Aligning with groups such as the ACLU, the Center for American Progress, Families Against Mandatory Minimums, the Coalition for Public Safety, and the MacArthur Foundation, Koch believes the current system has unfairly targeted low-income and minority communities all while wasting substantial government resources.

In an interview with Warren Cassell Jr., which was recorded in February 2016, Koch stated that as a child he did not live a privileged lifestyle despite growing up in a wealthy family. Koch said, “My father wanted me to work as if I was the poorest person in the world.” After attending several private high schools, Koch was educated at the Massachusetts Institute of Technology. He is a member of the Beta Theta Pi fraternity. He received a Bachelor of Science (B.S.) in General Engineering in 1957, a Master of Science (M.S.) in Nuclear Engineering in 1958, and a second M.S. in Chemical Engineering in 1960. His focus was on ways to refine oil.

In February 2016, Koch penned an opinion piece in The Washington Post, where he said he agreed with presidential candidate Bernie Sanders about the unfairness of corporate welfare and mass incarceration in the United States.

In June 2019, the Charles Koch Foundation announced the foundation of anti-war think tank Quincy Institute for Responsible Statecraft, cosponsored by George Soros’ Open Society Foundation. He is a board member at the Mercatus Center, a market-oriented research think tank at George Mason University.