Evan Greebel, a former corporate lawyer found guilty last year for helping “Pharma Bro” Martin Shkreli defraud a publicly traded pharmaceutical company, was sentenced Friday by a federal judge in Brooklyn to 18 months in prison.

Prosecutors from the Brooklyn U.S. Attorney’s office had sought no less than five years for Mr. Greebel, describing him as a “corrupt lawyer” who, as outside counsel to Retrophin Inc., abused his position as a lawyer to help Mr. Shkreli steal millions of dollars’ worth of cash and shares from the company...