Engineered living materials (ELMs) mimic the key characteristics of natural materials and are tailored to have enhanced non-natural functionalities. They contain cells that provide biological function and secrete an extracellular protein matrix that aids in their self-assembly and self-organization into multi-scale structures. Not only is the protein matrix essential in maintaining the structure of the living material, it enables the ability to tailor the bulk material properties for specific applications. However, few studies have focused on tuning the material properties of ELMs because this is a complex task that requires modulating the assembly of extracellular molecules. To address this knowledge gap, I explored how genetic and environmental modifications tune the bulk material properties using the bottom-up de novo engineered living materials (BUD-ELMs) platform in Caulobacter crescentus. First, I elucidated sequence-structure-property relationships in BUD-ELMs by changing the elastin-like polypeptide length within the extracellular protein matrix. I found fine-tuning genetic sequences in the protein matrix created significant differences in the microstructure and rheological properties of BUD-ELMs, revealing new design principles for creating living materials with tailored properties. Second, leveraging that the protein matrix contains exopolysaccharides (EPS), I evaluated how modifying the EPS and protein composition would tune the material properties using environmental modifications. I discovered that growing the BUD-ELM strain in sugar-based media formed de novo rope-like living materials that are strong and stiff with properties similar to elastomer and polymer-based materials. Lastly, I investigated how modulating the attachment of the protein matrix to the cells impacted the materials' properties by varying calcium concentrations in the growth conditions. I identified that microstructures with greater cell-matrix segregation led to bulk materials that are weaker, highlighting a simple strategy to significantly alter mechanical properties. Altogether, this thesis establishes a foundational framework for exploring structure-property relationships in ELMs to ultimately achieve rational material design and illuminates the transformative potential of de novo living materials in different applications, such as tissue engineering and drug delivery.