Mercedes said in a statement on Monday that Bell had resigned his position last December and would leave the team in November this year to pursue "new challenges outside the company".
Bell had been technical director since April 2011.
Mercedes said Lowe, who runs the team with fellow executive director Toto Wolff after the departure of principal Ross Brawn at the end of last year, would assume Bell's responsibilities without the role of technical director being replaced.
Lowe joined Mercedes from McLaren in June last year.
Mercedes have started the season in dominant fashion, winning the first three races with Nico Rosberg and Lewis Hamilton.
- Board & Management Changes
- technical director