Looking at the whole value stream from prospecting through project close-out you can see the key roles involved at different stages. It's important that the person in the lead at each stage has the right capabilities and is absolutely the right fit for the customer.
#1 MVP: Conceptual Estimator - Though they aren't in the lead at any stage; you can't underestimate how valuable their experience is when it comes to building a detailed cost and schedule model of the project based on very little information.
A great Conceptual Estimator can create this model with little more than a napkin sketch to start with then evolve the model over time as more information becomes available during design-development.
Senior Management is critical because they will have the ability to understand the perspectives of the owner including their buying motivations. They are needed to translate and integrate the higher-level thoughts of the project owner, architect and conceptual estimator.
The Project Manager who will ultimately be running the project should be brought in as early as practical so they start building relationships and ensuring that the design can be easily put into bid packages and built.
Every role on the team is critical at different points in the process.