Founder of the world's largest social networking site Mark Zuckerberg said the company had not expected to begin reaping financial benefits until sometime next year.
"This is important to us because it sets Facebook up to be a strong independent service for the long term," BBC quoted Zuckerberg as saying in a blog post.
"We are succeeding at building Facebook in a sustainable way. We are just getting started on our goal of connecting everyone.
"We face a lot of fun and important challenges that require rethinking the current systems for enabling information flow across the web," he added.
Mike Schroepfer, Facebook's vice president of engineering, also said, "Passing these milestones to me means we can continue to fund our development and our innovation and be self sustaining as we grow this network.
"We think 300m is a just a step on the way to get as much of the entire world on the social network communicating with the friends and family and the people they want to communicate with."
Nick O'Neill of AllFacebook.com added: "That Facebook is able to continue this growth and build a "cash flow positive" business is an impressive feat.
"If the company can cover the cost of scaling to 1 billion users and still manage to break even, there's no doubt that the company will have a great opportunity to rake in billions."
The news that the company had crossed the two benchmarks was made at TechCrunch 50 in San Francisco.