In more than 40 years of experience in legal profession, Leo Andreis practiced civil, criminal and commercial law, and he also participated in preparing various legal frameworks and contracts for the construction of power plants, financial and credit transactions with foreign banks and syndicates, foreign investments, privatization, legal due diligence and other legal matters.

Believing it is the obligation of every attorney at law to contribute to the development of the legal community as a whole, Leo Andreis has participated in the activities of the Croatian Bar Association for many years. He served as Secretary General of the Croatian Bar Association and was the President of the Croatian Bar Association. He was also the national representative of the Croatian Bar Association with the International Association of Lawyers - as National Vice President as well as Member of the Board of the International Association of Lawyers.