Living mulch (LM) provides many beneficial agro-ecological services by reducing soil evaporation, conserving moisture, controlling soil temperature, reducing weed growth, increasing organic matter and nutrient availability, and improving microbial activities. Legumes, commonly used as living mulches, can affect the yield and quality of main crops. We hypothesized that Egyptian clover co-cultivated with Cynara cardunculus var. altilis (cultivated cardoon) can positively affect both leaf biomass and phytochemical yield. The study was performed on two growing seasons of field experiments to evaluate the potential variation in biomass and phytochemical yields of cardoon leaves. In addition, the leaves were collected at 90, 120, and 150 days after transplanting to evaluate the possible effect of the harvest time. LM improved the fresh and air-dried leaves biomass yields, total phenolic, and dry matter content, while it had no effect on the content of crude fibre, total sugars, L-ascorbic acid, total chlorophylls, and antioxidant activity. Except for luteolin-7-O-glucoside content, no negative effect of LM was observed on the polyphenol profile. Behind the cultivation system, the parameters were also affected by both the harvest time and growing season. According to our data, the proposed intercropping of cultivated cardoon with LM could represent an innovative cultivation system to increase both leaf biomass and the health-promoting compounds of cultivated cardoon leaves by sustainable soil management.