Weisskopf previously served on the company's board of directors as vice chairman and was previously its CEO, Lindt writes in a press release.
Lechner is leaving the company after 33 years in various positions.
Lindt & Sprüngli needs new leadership to return to sustained, strong growth and seize all opportunities in its markets, the company writes in the press release.
The company is also dismissing Michal Spiller, head of its German operations. He will be replaced next week by Ali Kulein, currently head of Lindt & Sprüngli in Austria.