One significant challenge that plants, including those used in medicine and aromatics, face is their capacity to survive in unfavorable climatic conditions, particularly those associated with climate change. The main goal of this study was to assess the influence of temperature (15 and 30 °C for a period of two weeks) and UV-B radiation (4 hours per day and 4 hours every four days) on the biochemical and phytochemical responses of Lavandula viridis L’Hér and Thymus lotocephalus López and Morales. Following exposure to stress conditions, an evaluation was conducted of the photosynthetic pigments, oxidative stress level (H₂O₂ and MDA contents), soluble sugars, and phenolic profile and associated antioxidant activity. Plants cultivated under standard non-stressful conditions served as the control group. It was observed that both temperature treatments resulted in the highest oxidative stress in the plants, as evidenced by the H₂O₂ and MDA concentrations, which had a direct negative impact on the total chlorophylls and carotenoids. The data demonstrate that soluble sugars, phenolic compounds, and the related antioxidant activity play an important role in protecting both species from the oxidative stress caused by temperature and UV-B treatments. The highest content of the major phenolic compound of both species, rosmarinic acid, was produced in L. viridis exposed to 30 ºC (68.9 g/kg, representing a 68% increase over the control) and in T. lotocephalus following exposure to UV-B radiation for 4 h/4 days (26.6 g/kg, representing a 9.1% increase over the control). The findings of this study provide new insights into the responses of soluble sugars and phenolic compounds to unfavorable environmental conditions in L. viridis and T. lotocephalus plants. Furthermore, the findings contribute to the development of appropriate cultivation techniques for these plants, which may be employed for industrial or other purposes.