Staff Machine Learning Engineer

Apollo.io is the leading go-to-market solution for revenue teams, trusted by over 500,000 companies and millions of users globally, from rapidly growing startups to some of the world's largest enterprises. Founded in 2015, the company is one of the fastest growing companies in SaaS, raising approximately $250 million to date and valued at $1.6 billion. Apollo.io provides sales and marketing teams with easy access to verified contact data for over 210 million B2B contacts and 35 million companies worldwide, along with tools to engage and convert these contacts in one unified platform. By helping revenue professionals find the most accurate contact information and automating the outreach process, Apollo.io turns prospects into customers. Apollo raised a series D in 2023 and is backed by top-tier investors, including Sequoia Capital, Bain Capital Ventures, and more, and counts the former President and COO of Hubspot, JD Sherman, among its board members.

About Apollo

Apollo.io is the leading go-to-market platform for revenue teams, trusted by over 500,000 companies and millions of users globally. We provide sales and marketing teams with easy access to verified contact data for over 210 million B2B contacts and 35 million companies—plus the tools to engage and convert them all in one place.

As an AI-native company, we are redefining how businesses drive pipeline and revenue. Backed by top-tier investors like Sequoia Capital and Bain Capital Ventures, and recently valued at $1.6B, Apollo is one of the fastest-growing SaaS companies in the world.

Your Role & Mission

We are looking for a Staff Machine Learning Engineer to join our growing Intelligence team. You will lead mission-critical initiatives that power ML-driven user experiences across search, recommendations, content generation, scoring, and more. Your role is to push Apollo forward as an AI-native product, helping us create intelligent, personalized, and highly automated features that scale.

You will collaborate closely with engineers, product managers, and data scientists to build machine learning systems that enhance Apollo’s ability to guide our users to value—and drive the future of our AI platform.

Responsibilities:

• Design, build, evaluate, deploy and iterate on scalable Machine Learning systems

• Drive end-to-end ML initiatives—problem definition, data exploration, modeling, productionization, and monitoring.

• Understand the Machine Learning stack at Apollo and continuously improve it

• Lead development of intelligent features powered by LLMs, embeddings, ranking models, and semantic search.

• Guide platform architecture decisions and contribute to foundational ML infrastructure (e.g., feature stores, MLOps).

• Work cross-functionally to define AI-first product experiences and rapidly iterate toward user impact.

• Mentor and uplevel engineers across the org, influencing engineering best practices and technical direction.

• Champion the use of AI internally to drive engineering and operational efficiency.

Required Qualifications: 

• 8+ years of experience building and scaling machine learning systems in production environments.

• Strong experience with LLMs and embeddings (e.g., fine-tuning, prompt engineering, vector databases).

• Hands-on experience with Python and modern ML libraries such as PyTorch, TensorFlow, HuggingFace, or Scikit-learn.

• Experience with cloud infrastructure (e.g., GCP), orchestration (Airflow), and experimentation platforms (e.g., mlflow, Databricks).

• Excellent collaboration and communication skills—can influence across product and engineering teams.

• Proven impact shipping ML-driven features in B2B SaaS products or enterprise platforms.

Preferred Qualifications:

• Bachelors, Masters, or a PhD in Computer Science, Mathematics, Statistics, or other quantitative fields or related work experience

• Experience with retrieval-augmented generation (RAG), search infrastructure, or recommendations at scale.

• Exposure to GTM, marketing tech, or sales enablement domains in a B2B setting.

We are AI Native

Apollo.io is an AI-native company built on a culture of continuous improvement. We’re on the front lines of driving productivity for our customers—and we expect the same mindset from our team. If you're energized by finding smarter, faster ways to get things done using AI and automation, you'll thrive here.

Why You’ll Love Working at Apollo

At Apollo, we’re driven by a shared mission: to help our customers unlock their full revenue potential. That’s why we take extreme ownership of our work, move with focus and urgency, and learn voraciously to stay ahead.

We invest deeply in your growth, ensuring you have the resources, support, and autonomy to own your role and make a real impact. Collaboration is at our core—we’re all for one, meaning you’ll have a team across departments ready to help you succeed. We encourage bold ideas and courageous action, giving you the freedom to experiment, take smart risks, and drive big wins.

If you’re looking for a place where your work matters, where you can push boundaries, and where your career can thrive—Apollo is the place for you. 

Learn more here!