To measure the effect of organic food conversion projects on the percentage of organic food used in Danish public kitchens participating in the Danish Organic Action Plan 2020. The current longitudinal study was based on measurements of organic food percentages in Danish public kitchens before and after kitchen employees participated in conversion projects. Public kitchens participating in the nine organic food conversion projects under the Danish Organic Action Plan 2020, initiated during autumn 2012 and spring 2013 and completed in summer 2015. A total of 622 public kitchens. The average (median) increase in organic food percentage from baseline to follow-up was 24 percentage points (P<0·001) during an overall median follow-up period of 1·5 years. When analysing data according to public kitchen type, the increase remained significant for seven out of eight kitchens. Furthermore, the proportion of public kitchens eligible for the Organic Cuisine Label in either silver (60–90 % organic food procurement) or gold (90–100 % organic food procurement) level doubled from 31 % to 62 %, respectively, during the conversion period. Conversion project curriculum mostly included elements of ‘theory’, ‘menu planning’, ‘network’ and ‘Organic Cuisine Label method’ to ensure successful implementation. The study reports significant increases in the level of organic food procurement among public kitchens participating in the Danish Organic Action Plan 2020. Recommendations for future organic conversion projects include adding key curriculum components to the project’s educational content and measuring changes in organic food percentage to increase the chances of successful implementation.