[5] Willink co-authored the books Extreme Ownership and The Dichotomy of Leadership (with fellow retired SEAL Leif Babin) and co-founded the management consulting firm Echelon Front, LLC.

[8] Following SEAL tactical training (STT) and completion of six-month probationary period, he received his trident insignia.

Willink was part of the SEAL team that seized the Russian Tanker Volga-Neft-147 in the Gulf of Oman, which was carrying Iraqi oil in violation of a United Nations economic embargo.

[9][failed verification] Willink earned his commission via Officer Candidate School and served as a platoon commander.

[6] During Operation Iraqi Freedom he deployed to the Iraqi city of Ramadi in 2006 with SEAL Team Three as commander of Task Unit Bruiser, which included Leif Babin, Seth "Stoner" Stone, Marc Alan Lee, Michael Monsoor, Jonny Kim, Kevin Lacz, Ryan "Biggles" Job, JP Dinnell, Tony Eafrati, Jason Hogan and Chris Kyle.

[10] After retiring from the Navy, Willink co-founded the leadership consulting firm Echelon Front along with Leif Babin, who served with him in the SEAL Teams.

[13] In addition to his work in consulting and authorship, Willink instructs jiu-jitsu at Victory MMA & Fitness in San Diego and co-owns Origin USA, a company based in Farmington, Maine, which produces lifestyle apparel, nutrition supplements, and fitness equipment,[14] as well as being one of the only manufacturers of jiu-jitsu gis in the United States.

Willink started Brazilian jiu-jitsu under Fabio Santos while in active service and continued training after retirement from the military.

[20] In 2017, he published Discipline Equals Freedom: Field Manual, which is a collection of healthy living routines and mindsets for productivity.