Lassie holds a BProc degree from the University of Limpopo, LLB degree from the University of South Africa, a diploma in Leadership, Financial Management and Communication under the auspices of USSALEP, Certificate in Mediation and Arbitration with AFSA and a Certificate in Court-Annexed Mediation with L.E.A.D. He was admitted as an attorney in 1983 and practised in one of the first “black” firms of its size in Pretoria at that time. He was the chairperson of the Law Students’ Council in 1996 while he was at university. Lassie is a founding member of the Democratic Lawyers Congress in Pretoria, which in turn founded the current National Association of Democratic Lawyers (NADEL). He was a member of a technical team established by Nelson Mandela to set up government and administration structures in Limpopo in 1994. Lassie became the first chairperson of the Northern Province Casino and Gambling Board and founding member of the Southern African Gaming Regulators Association. He was a special adviser to the first and second premiers of Limpopo from 1994 up to June 2006 and a member of the Provincial Constitutional Technical Committee that advised and assisted the Constitutional Assembly to draft the new Constitution in South Africa. Lassie became a member of the Judicial Service Commission representing the premiers of Limpopo in the appointment of judges. He was a founder member and director of Mahlangu Attorneys that merged with MacRobert Incorporated in 2015.