Senior Full-Stack Engineer, SaaS at Mercor

Senior Full-Stack Engineer | $75–95/hr | Remote (US) | W-2 Full-Time via Cincinnatus LLC

We are looking for a seasoned Senior Full-Stack Engineer to lead the architecture and development of a multi-tenant SaaS platform serving regulated financial and government procurement workflows. If you've been the lead or sole developer on a non-trivial SaaS product and thrive on making end-to-end architecture decisions, this role is built for you.

Key Responsibilities

• Platform Architecture: Own architecture decisions across frontend, backend, data, and infrastructure for a multi-tenant SaaS product, balancing configurability with long-term maintainability.
• Tenant-Level Configurability: Build admin-managed configuration for fee models, reporting periods, grace periods, escalation rules, branding, and integrations — no code changes required per tenant.
• RBAC & Multi-Portal Access: Design and maintain role-based access control across distinct user populations (internal ops, external vendors, government customers) with separate permission matrices per portal.
• Financial Engines: Build and maintain fee calculation engines supporting percentage, flat, capped, and tiered models with deterministic rounding; deliver audit-ready exports at penny-level precision.
• Payment Lifecycle & Reconciliation: Implement payment lifecycle tracking, cash reconciliation, and exception handling against external payment systems.
• Integrations: Integrate payment processors, procurement ERPs, CRM systems, and notification services; experience with government payment gateways is a plus.
• Intake Pipelines: Build file upload processing, cross-field validation, cross-role alerts, and configurable period enforcement for structured intake workflows.
• Compliance & Escalation Workflows: Build configurable engines for delinquency rules, notification tiers, communication templates, and grace period management.
• Cross-Functional Collaboration: Partner with product, ops, and compliance stakeholders to translate regulatory and contractual requirements into shippable software.

Core Qualifications

• 5+ years of professional full-stack engineering experience, with 2+ years as a lead or sole developer owning architecture on a production SaaS product.
• Proven experience building multi-tenant SaaS with tenant-level configurability managed by admins without code changes.
• Experience with RBAC spanning internal operators, external vendors, and end customers with separate permission matrices per portal.
• Background in financial software: fee calculation engines, payment lifecycle tracking, cash reconciliation, and audit-ready exports.
• Hands-on experience integrating payment processors, procurement ERPs, CRM systems, and notification services.
• Experience building intake pipelines with cross-field validation, cross-role alerts, and configurable period enforcement.
• Experience building compliance or escalation workflow engines (delinquency rules, notification tiers, grace period management).
• Strong written and verbal communication; able to drive technical decisions independently and document tradeoffs clearly.

Preferred Qualifications

• Experience with government procurement or regulated financial compliance platforms.
• Familiarity with government payment gateways such as Tyler/NIC or similar.
• BI embedding experience (PowerBI, Jaspersoft, or similar) with row-level data isolation across tenants.
• Experience exposing platform functionality to an agent layer through a typed SDK or API.

About the Employer

This is a W-2 full-time position employed by Cincinnatus LLC, an enterprise staffing company that partners with leading technology companies to place highly skilled professionals within client teams. Cincinnatus serves as the employer of record, providing payroll, benefits, and compliance support while you integrate directly into a client's team on high-impact work.

Cincinnatus LLC is an Equal Employment Opportunity employer and is committed to providing reasonable accommodations for qualified individuals with disabilities throughout the hiring process.