Thorntons, who are one of the leading brands in the luxury chocolate market, has been struggling with waning sales since the start of the year and posted poor performances in both interim and annual results.
Current restructuring moves at the company could see profits picking up however as a number of top management positions are filled.
In June, John von Spreckelsen from UK supermarket chain Somerfield, joined Thorntons as the group's chairman.
And the company recently announced the appointment of Paul Wilkinson as independent non-executive director.
Previously Wilkinson held the executive chairman position at one of the UK's top bakers RHM.
John Thornton's decision to retire leaves no Thorntons family member on the board and follows in the footsteps of his brother Michael who left three years ago.
The family will continue to hold around a 22 per cent stake in the company according to the Financial Times.
Thorntons, which was founded in 1911, is different from most chocolate companies in that it manufactures and sells its product through its own network of shops and franchises.
In recent months the company has concentrated on improving its profitable Thorntons Direct business - an online shopping service.
With the launch of a new website and more concentrated advertising Thorntons hope to increase the popularity of the site.