Currently, the effects of global warming are one of the most important topics on the agendas of all governments and international economic and scientific organisations on the planet. Temperatures and rainfall will be especially subjected to increasing deregulation, and thus crop yields will be affected according to geographic location. Cellulosic materials, such as bast fibres, are considered one solution to decrease human environmental impact: they are a renewable resource, biodegradable and have a lower carbon emission than synthetic materials. However, their quality, yield and mechanical properties depend on environmental conditions during plant growth. In this paper, we explored the possible impact of seasonal drought linked to future climate change on flax plants and fibre quality. Two batches of the same textile flax plant cultivar were grown under two different field environmental conditions in the same year, one taken as a control under regular climatic conditions and the second one grown under drought stress. Carbon isotopic discrimination reveal an increase in water stress plant of the fibre δ13C, reflecting that plants are indeed suffering from drought stress from a physiological point of view. We characterized the mechanical properties, biochemistry and morphology parameters at both the stem and technical fibre scales. Our results showed that the plants of the two batches were morphologically different and that the drought-stressed plants were smaller, mainly in terms of the height of the stem (−28%) and diameter (−16%). Biochemical analyses highlighted a contrasting lignin content between the two batches. A difference in protein content was also measured, with an increased amount in stressed flax plants, with contrasting distributions revealed by tyrosine and tryptophan monitored by synchrotron UV fluorescence. In addition, polysaccharide composition was also quantified with an increase in mannose and an important decrease in glucose in the drought-stressed technical fibres. Surprisingly, despite the difference in biochemistry composition and morphological parameters, the mechanical properties of elementary flax fibres extracted from the two batches were not significantly different. This suggests that drought can affect the yield and biochemistry of the extracted technical flax fibres but does not necessarily impact the longitudinal mechanical performance of single fibres.