This study evaluates labour market flexibility using the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS), a multi-criteria decision analysis (MCDA) method. TOPSIS is employed by comparing spatial (i.e., different countries) and temporal (i.e., long-time horizon) terms. Sustainable industrial relations processes are considered in shaping the flexibility of the labour market in 15 European Union Member States from 2009 to 2018. Countries are grouped into classes to provide a basis for benchmarking results against social and employment policies implemented at the national level. A five-step quantitative MCDA method is formulated using published data from the Organisation for Economic Co-operation and Development. The results indicate that the TOPSIS method is an appropriate approach for measuring labour market flexibility internationally. Moreover, in relation to workforce phenomena, the findings show that the method offers the possibility of examining the impact of particular factors related to social and employment policies of a country in terms of sustainable development and socioeconomic growth. The lack of precision tools to forecast the development of national and transnational labour markets—particularly during the COVID-19 era—highlights the importance of such a method for workforce planners and policymakers. Developing sustainable industrial relations in terms of associated national externalities is the motivation of the research.