Health and wellness tourism is growing worldwide, triggering a resurgence of competition in this segment and a clear need for the supply to develop new products and services, increasingly creative and exclusive, capable of attracting tourists. Thermal waters in Portugal are considered very rich in terms of chemical composition, which makes their use highly important in various wellness and rejuvenating therapies like balneotherapy, thermalism, etc. This enables the country to pursue a differentiated wellness-related experience product, which is a key determinant of customer loyalty and can play an important role in regional development. Natural resources contribute to the strengths of territories and can be leveraged by marketing tools such as brands. This article intends to draw inferences about the effect of the brand on the competitiveness of the wellness tourism supply, across NUTS II regions of the continent, during the period of ten years, with a special focus on the recent period of the COVID-19 pandemic. With a sample of 10 spas in Portugal, retrieved from SABI database, we analyze the evolution of four competitiveness indicators: market share, productivity, return on investment and talent retention, for 2010–2020, by clusters of firms with and without brand. The correlation analysis between brand and competitiveness indicators suggests a strong positive and significant relationship between brand and market share, in the Centro and Lisbon regions, starting in 2017 and increasing over time. Finally, some recommendations on tourism management are made to improve the competitiveness of the supply.