He is the founder and Executive Chairman of Keller Williams, which is the largest real estate company in the world by agent count and second in closed sales volume, and units sold.

[5] While at Baylor, Keller spent time shadowing professionals in the fields of law, accounting, banking, and real estate.

[10] In 2017, he began to transition Keller Williams into more of a technology company,[11] launching technology initiatives that included KW Labs, KW Keller Cloud, and "Kelle," an artificial intelligence app used as a virtual assistant and an agent-to-agent referral tools platform called "Referrals.

His first book, The Millionaire Real Estate Agent, was co-authored with Dave Jenks and Jay Papasan and released in 2004.

[16] In 2013, Keller and co-author Papasan published their first non-real estate book, The ONE Thing: The Surprisingly Simple Truth Behind Extraordinary Results.

[21] Keller is also a public speaker[22] and was a panelist for the nonprofit Relationship & Information Series for Entrepreneurs in 2013 along with former Texas Longhorns quarterback Vince Young.

[23] In 2013, Keller launched ALL ATX, a nonprofit with a goal to educate musicians on how to build successful careers in the Austin music industry.

[28] Keller teaches a business and life development course to young adults both in Austin and through his alma mater, Baylor University.

He has been a supporter of Baylor since his graduation, and in 2007 he donated the funds for a residential real estate research center at the Hankamer School of Business.

[29] The Keller Center, as it was named, studies consumer behavior, marketing strategies, and management solutions.