Osman has many years of professional experience as a lawyer, especially in the field of immigration law. Already as a student he gained experience in immigration law at the law firm Fragomen.  As a student he also worked voluntarily as a council board member, where he gained experience in public law. He negotiated with the authorities and helped clients from Germany and abroad with their applications to the authorities.

During his time at the German-Malaysian Chamber of Commerce and Industry (MGCC) in Kuala Lumpur, Osman was able to gain further professional experience. As a member of the legal department, he advised Malaysian companies and businesspersons on their planned investments in Germany and German companies and businesspersons on their planned business activities in Malaysia.

At EY Law (Ernst & Young), Osman has advised many global companies on the design and implementation of secondment programs. In his daily work, he advised human resources departments on legal and strategic issues. He advised the employees of these companies on the legal aspects of the right of residence for themselves and their families. He advocated to the German authorities for the implementation of his clients' rights. Osman worked closely with the teams from employment law and company law when it came to founding new subsidiaries and drafting employment contracts.

In his next position, he worked as a project manager for a US eDiscovery & legal consulting company on a project with more than 20 lawyers. In his role as project manager, he oversaw the work of his team and coordinated the results with the client law firm.  He was also the designated contact for the German office of this US company.

In 2017, Osman founded leaves and trees | Rechtsanwaltskanzlei and began to offer his services in the areas of immigration law, labor law and corporate law.

In 2018/2019 Osman advised an Intergovernmental Organization for a longer period of time, in particular on residence law and labour law. During the consultation on international law, Osman dealt in particular with the Protocol on Privileges and Immunities and the Headquarters Agreement which the Organization had agreed with the government. He advised the Organization on the rights and obligations for the Organization and its staff arising from the agreements with the government in interaction with the laws in force in Germany.

Osman today consults individuals, entrepreneuers, as well as the human resources departments of larger companies.

During Osman's professional experience he has advised many companies from all over the world. He was especially responsible for companies from the USA, Canada, Mexico, Brazil, India, China, Japan, South Korea, Malaysia, Indonesia, Singapore, Russia, UAE, Jordan, Turkey, Israel, South Africa, Morocco, Australia and some more.

He has advised multinational companies, mid sized companies as well as entrepreneurs and start-ups. Some areas Osman has advised: