Stegelmann will be responsible for the 'Global Partnership Acquisition' at the team and its fashion branch.
Stegelmann previously worked as Chief Commercial Officer of the Motorsport Network, later managing the sales team of ITR, which organised the DTM series until 2022.
He was also involved in the sales and marketing concept, development and implementation of Formula E.
Before that, his work included sales activities in the 2010 World Cup in South Africa and the European football association UEFA.
"Interest in Formula 1 has developed extremely well. With the support of Lars, we also want to develop our commercial activities," said AlphaTauri team boss Franz Tost.
"He has an exciting mix of strategic know-how, international sales experience and a great understanding of the advertising industry."
Stegelmann added: "Formula 1 is booming and is offering companies excellent activation and communication opportunities, premium hospitality and awareness on a global scale like no other sport series.
"The various stakeholders, especially the advertisers and agencies, have been my clients for many years.
"The positioning of Scuderia AlphaTauri fits perfectly into the current times and offers a first-class platform for companies that want to appear modern, young and dynamic, digital, design and technology-oriented.
"I look forward to making my contribution to further global development."
