Caldwell steps up to the Formula 1-supporting series after finishing fifth in the Formula Regional European Championship last year, scoring one victory and eight podium finishes.
The 17-year-old appeared for Trident at the post-season rookie test in Valencia in October, before representing the squad in the Macau Grand Prix.
He will be joined at the Italian outfit by former Charouz driver Lirim Zendeli and Devlin DeFrancesco, the latter having been retained by the team for another season.
“I am very happy to be joining Trident this year in FIA F3,” Caldwell said. “The team has the capability to win races and I’m looking forward to pushing the car to the limit and collecting trophies for them.”
Trident finished fourth out of 10 teams in F3 last season, with former Pedro Piquet scoring the team’s only victory at Spa in a year dominated by Prema.
Team Principal Maurizio Salvadori said: “Olli Caldwell is one of the most promising and appreciated prospects in British motorsport. We had the chance to evaluate his skills and qualities last year in post-season testing at Valencia and in the Macau Grand Prix.
“Despite being a rookie, Caldwell impressed our technical staff on both occasions. I am sure that all the right ingredients are in place for him to do extremely well with Team Trident, which will give its 100 per cent to support him in such a competitive series like the FIA Formula 3 Championship.”
Team Manager Giacomo Ricci added: “By announcing Olli Caldwell, we are finally completing our FIA Formula 3 Championship line-up for 2020. This is a very challenging series in which he will join Devlin Defrancesco and Lirim Zendeli, who both are at their second season.
“Caldwell impressed the team's staff for his technical and sportsmanship skills. He is extremely promising and professional. I am sure that we got all the best foundations for a positive and exciting season.”
Earlier this week, Jenzer announced Federico Malvestiti as its third driver for the 2020 season. He will partner Matteo Nannini, nephew of grand prix winner Alessandro, and Calan Williams.
2020 FIA F3 grid so far:
ART Grand Prix