Jennings was born in England and met production partner Nick Goldsmith while the pair were attending art school. In 1999, they launched their production company Hammer & Tongs, with a mission to put together a solid creative team, have some fun, and make cool music videos that would hopefully get aired on MTV. For the next decade, they built a dependable reputation and an enormous client reel with their uniquely styled and often humorous videos, including Fatboy Slim's "Right Here, Right Now," REM's "Imitation of Life," and Blur's "Coffee and TV" (in which an ambitious milk carton heads off in search of the missing child on its side). Hammer & Tongs also took on an increasing number of commercial clients, but had no intention of transitioning into feature film production, when they were first presented with a script for "The Hitchhiker's Guide to the Galaxy," a project which had been passed onto them following a recommendation by director Spike Jonze. The Douglas Adams' sci-fi franchise had sold over 15 million copies as a book and already been adapted into comic books, radio, television shows and even video games. Despite concerns about tackling something so well-known and doing it justice within the Hollywood system, the pair quickly storyboarded the script that Adams had penned prior to his untimely death, and in record time, won Disney over with their presentation. Jennings was signed onto direct, and Goldsmith to produce. The meticulously designed film was a hit with Adams' cult fans and average moviegoers alike. Jennings was also praised for maintaining the author's particular British sensibilities, especially with his choice of opting for Henson puppets over slick computer-generated animation.In early 2007, Jennings completed "Son of Rambow," the first feature he both wrote and directed. The film revolved around a pair of boys in the 1980s who use a home video camera to make their own sequel to the Sylvester Stallone vehicle, "Rambo: First Blood" (1982). "Son of Rambow" created a huge stir at the Sundance Film Festival in January, where a bidding war ensued over the film's distribution rights, which reportedly sold for over seven million dollars. But the theatrical release belied such an up-front expense, as the film made less than $2 million at the box office. Returning to what they did best, Hammer & Tongs directed several more music videos, including Radiohead's "Jigsaw Falling Into Place" (2007), "Nude" (2008), and "Lotus Flower" (2011), and Vampire Weekend's "A-Punk" (2008) and "Cousins" (2009). While Jennings branched out on his own to voice Bean's Son in Wes Anderson's animated feature "The Fantastic Mr. Fox" (2009), Hammer & Tongs announced in June 2012 on their website Tongsville that the pair were splitting after 17 years together. No reason for the breakup was give outside of announcing that they were pursuing separate ventures.