Chief Justice Beverley McLachlin, the first woman to become Canada’s top judge, will step down this December after serving a record 18 years in the job, the Supreme Court said on Monday. McLachlin, 73, presided over a series of landmark rulings on topics such as same-sex marriage and prostitution and clashed on occasion with the former Conservative government of Prime Minister Stephen Harper, which felt the court had become too activist.She joined the top court as a judge in 1989 and became chief justice in January 2000. She would have reached the mandatory retirement date of 75 in September 2018.”She has been a judicial leader and trailblazer for almost four decades … her contributions reach into every part of our law,” Liberal Prime Minister Justin Trudeau said in a statement.The court declined to comment when asked about the reasons for her retirement.Under McLachlin, the court allowed same-sex marriage and supervised injection drug clinics and physician-assisted suicide. It also struck down major restrictions on prostitution.In 2014, it barred a Harper nominee from taking a job at the court, citing the candidate’s lack of qualifications. The episode triggered a public dispute between the prime minister and chief justice.At a rare news conference in August 2015, she dismissed the idea the court had become too activist.”We try to answer the questions put before us in accordance with the constitution and the law. I leave the labels to other people,” she said.