In parallel with his education at school and university, Stefan Mittmann started working as a field applications engineer for microcontroller systems at the company P. Caritato and Associated in Athens. The company was representing leading electronic component manufacturers, such as Texas Instruments, National Semiconductor, DuPont, Murata and others in Greece. In 1983 he becomes a partner at the company, which was later transformed into a Societe Anonyme.

Between 1981 and 1986 he completed more than 30 commercial projects based on the microcontroller COP402 manufactured by National Semiconductor for a large number of clients in Greece, including a complex telephone exchange system for the company Standard Electric Hellas.

In 1986 he successfully completed the firmware for the first masked programmed microcontroller applications in Greece, a remotely controlled car alarm system for the company TIGER Electronics, which had significant success and was manufactured in high volumes for Greece and exports to a number of countries, including Germany.

In 1987 he assumes the position of Sales Manager and subsequently General Manager of the company.

In 1990, Stefan Mittmann started working as a purchasing manager at the company INTRACOM. His main task was to setup the effective sourcing of components for the  development of the company´s new competitive and export oriented products.

Over the next years, he expands and organizes the purchasing department, which by the year 2000 employed more than 50 purchasing professionals, handling a yearly procurement volume in excess of 200 billion Drachmae (approx. 600 million Euros)  from more than 2.500 suppliers in Greece, other European countries, the USA and the Far East.

Furthermore, he has a significant contribution in building strong relationships with strategic suppliers, such as CISCO, SUN Microsystems, SAP, Hewlett Packard, Ericsson, Motorola, Oracle, Raytheon and many more.

During the period 2001 up to 2004, Stefan Mittmann is being appointed Corporate Liaison Officer with a focus on the subsidiary company Fornax in Hungary, ensuring its cooperation with the other companies of the Intracom group and becomes a member of its Supervisory Board.

In 2003 he joins the newly established Subsidiaries and Participations Division of the Intracom Group and participated in the preparation of business plans for many companies of the Intracom Group.

In 2004, Stefan Mittmann is being appointed member of the Board of Directors of the investment brokerage company INTRAFIN, which was the first company of it´s kind to receive an operating license from the Hellenic Capital Market Commission. He closely monitors the development of listed companies in the Athens Stock Exchange. He is holding his position as a member of the Board of Directors of Intrafin until today.

During 2006, Stefan Mittmann is working as a qualified instructor for training seminars on procurement issues for the Hellenic Purchasing Institute and post graduate courses of the  University of Piraeus. 

In 2007 Stefan Mittmann establishes HELIOINDEX SA, as a joint venture with the Greek company Tesco. He assumes the position of the Managing Director and leads HELIOINDEX as a successful equipment distributor in the growing Greek photovoltaic (PV) market.

The track record of HELIOINDEX includes the first grid-connected PV system for own consumption (2007), the first free-field system installed using rammed piles, without a concrete foundation (2008), the first residential rooftop system in Athens (2009) and the largest PV system on an Aegean island, Santorini (2011). All activities of HELIOINDEX are sucessfully completed during 2012 and the company is put in liquidation upon a common decision of the founding partners.

Stefan Mittmann continues his activities in the PV market in cooperation with the German PV module manufacturer Solar-Fabrik and delivers PV equipment for a number of PV projects. He also acts as a strategy and project implementation consultant for other German companies in Greece.

With the Greek PV market showing strong trends of saturation in 2013, Stefan Mittmann decides to focus on his well-known activity of procurement and establishes a consulting office to offer his services to companies, which wish to exploit the opportunities provided by an advanced purchasing and supply management function.