He’s been on the FISA court since May 18, 2014. Roberts appointed him. Wikipedia says he dismissed a lawsuit in 2017 from Electronic Privacy Information Center (EPIC), who was suing the IRS to get Trump’s IRS Returns. On March 27, 2019, Boasberg blocked a work requirement for recipients of Medicaid in Arkansas and Kentucky.
You are correct. Boasberg is a lefty, but a rare one with some solid judicial probity ...