Howell was promoted into F1's global comms hot seat in February 2017 after spending nearly two years as its head of digital.
He reported directly to MD of commercial Sean Bratches and was appointed to the newly created position after Liberty Media acquired the business.
Formula One confirmed Howell's departure to PRWeek and said the comms team is being restructured. Instead of a director of communications, there will be a head of corporate and consumer communications and a head of motorsport press office.
Both of these roles will report into F1 director of marketing and communications Ellie Norman.
Howell led digital and communications at Formula One through the transition from Bernie Ecclestone’s ownership to Liberty Media, which acquired the racing car series in a $4.8bn acquisition in early 2017.
Howell made the announcement on his LinkedIn page, saying: "Have now left Formula 1 after covering the digital and communication roles through the transition from Bernie Ecclestone’s FOM to the present ownership of F1 by Liberty Media.
"I will take a short break and some thinking time before plunging headlong once more into the very exciting and ever-changing world of content communications."
Howell has more than 30 years of experience in PR and communication, including several roles in motorsports.
At the time he was promoted to global comms director in 2017, Bratches said: "His extensive and demonstrated experience leading communications strategies for many of the world’s most prestigious motorsport brands, together with his background as a journalist and social media specialist, align well with our objectives to broaden Formula 1’s appeal and proactively engage the marketplace to elevate the exciting changes that we are envisioning and implementing."
Prior to joining F1, Howell was head of sport at Pulse Films and has previously headed comms at the Ultimate Fighting Championship, the Fédération Internationale de l'Automobile (FIA). He was also publisher and editor in chief of Red Bull’s Red Bulletin magazine.
He first joined Formula One in 2003, when he spent a year as its media director.