A Matplotlib developer utilizes the Matplotlib library in Python to generate data visualizations, such as diagrams and graphs. They convert large and complex datasets into easily understandable visual representations, like bar graphs, histograms, pie charts, scatter plots, etc. Their role involves understanding the data, choosing the appropriate type of plot, customizing the design of the plot for better readability, and troubleshooting issues in the visualization. They may also need to work with other data analysis libraries like NumPy or Pandas, and present the visualized data in a way that it can drive decision-making processes.