This project first surfaced back in 2014, when Imperative Entertainment acquired the rights to a June 2014 New York Times Magazine article entitled "The Sinaloa Cartel's 90-Year-Old Drug Mule" by Sam Dolnick. The production company had set Ruben Fleischer (Zombieland) to direct the movie while looking for a writer to adapt this incredible true story. While Ruben Fleischer is no longer involved, this new report reveals that Nick Schenk, who wrote the script for Clint Eastwood's 2008 drama Gran Torino, wrote the original draft of The Mule, with Dave Holstein (Weeds, The Brink) rewriting the script.

In 2011, at the age of 87, Leo Sharp was arrested by Michigan State Police, while in possession of more than 200 pounds of cocaine. For just under a decade, he was one of the most prolific drug mules for the Sinaloa Cartel, lead by the infamous El Chapo. DEA agents had tracked him down through wiretapped phone conversations with cartel leaders, who only identified this drug mule by the nickname "Tata," the Spanish word for "grandfather." Not only did Leo Sharp have no criminal record before this arrest, he was a decorated World War II veteran who received the Bronze Star Medal for his service, and later became a world-renowned horticulturist, best known for creating new hybrids of flowers. The the daylily "Hemerocallis 'Siloam Leo Sharp'" is named after him.

At his trial, his defense team argued that Leo Sharp had suffered from dementia, which set him down this unlikely path to become the most prolific drug courier in Detroit for a massive drug cartel. The judge issued a three-year prison sentence on his 90th birthday, after his defense stated that he would not do well in prison with his dementia. In June 2015, prosecutors convinced a Detroit federal judge that he should be released early, due to his declining health. He was said to have a terminal illness and was not expected to live more than six months, but upon his release from prison, he lived for more than a year and a half, before dying in December 2016, at the age of 92.

Clint Eastwood had been working on the Jessica Buchanan biopic entitled Impossible Odds in late 2016, but he dropped everything to direct his new film The 15:17 to Paris, which explores the true story of the three Americans (Spencer Stone, Anthony Sadler and Alek Skarlatos) who thwarted a terrorist attack on a Paris-bound train in 2005. The director made the bold move of casting the actual heroes to play themselves in the film, which is slated to hit theaters February 9. The Tracking Board broke the news on The Mule.