james s. cowan, cm qc (born january 22, 1942) is a canadian lawyer, a senator from nova scotia from 2008 to 2017, and was leader of the opposition in the senate from 2008 to 2015 and leader of the independent liberal caucus until june 15, 2016. a lawyer, cowan has been a partner at the legal firm of stewart mckelvey since 1967. he retired from the senate on january 22, 2017, having reached the mandatory retirement age for senators.