Duolingo Inc., a language-learning platform that has amassed more than 1 million paid subscribers and has a $1.5 billion valuation, has found its first general counsel.

The Pittsburgh-based venture capital-backed startup named Stephen Chen as its top lawyer on Tuesday. An in-house tech veteran with extensive dealmaking experience, Chen has worked in the legal departments of Yahoo, VMWare Inc., Marin Software and, most recently, Proofpoint Inc., a cybersecurity software company in Silicon Valley. 

"Having spent most of my career working at tech companies in Silicon Valley, I am looking forward to relocating to Pittsburgh for this new opportunity to build out the legal function with one of the city's most successful startups," Chen said in a statement. "Personally, I love how the app helps me connect with my cultural identity and learn the language my parents speak."

Chen joins Duolingo as the company, which has also hired its first chief financial officer, experiences significant growth. 

In December, the firm announced that it had raised $30 million in funding from CapitalG, the investment arm of Google parent company Alphabet Inc. The investment brought Duolingo's funding up to nearly $140 million and raised its valuation from $700 million to $1.5 billion.  

In announcing the new GC and CFO hires, Duolingo CEO and co-founder Luis von Ahn stated that he expected to increase the company's employee head count by 50% this year "as we prepare for our next phases of business growth."

Stephen Chen, general counsel at Duolingo.

Chen had worked in Proofpoint's legal department since 2014 and helped the firm implement a companywide compliance training program; acquire more than a dozen companies; and form and manage subsidiaries throughout the Middle East, Europe and Asia, according to his LinkedIn profile. He was not immediately available for an interview. 

At Yahoo and VMWare, where Chen served as legal director and senior counsel, respectively, he oversaw acquisitions, investments and joint ventures. He joined Marin in 2012 as associate general counsel and led the legal effort behind the San Francisco-based online advertising firm's initial public offering in 2013. 

A Harvard Law School grad, Chen began his legal career in 1997 as an associate at O'Melveny & Myers. He left private practice in 2000 and joined venture-funded startup Hiwire as one of two in-house lawyers. He departed Hiwire after a year and returned to O'Melveny, where he stayed for more than four years before going back in-house for Yahoo.