The Vistaprint-owner, which announced the £66m purchase of a majority stake in Exaprint earlier this month, will pay a base purchase price of €23.3m (£17.2m) for Druck.at including €20m payable in cash and a €3.3m deferred payment payable in cash or stock no earlier than 2017.
Cimpress said the acquisition supported its strategy to "leverage a common platform across multiple brands, each with a distinct value proposition and customer focus".
Cimpress chief executive Robert Keane said: "We believe Druck.at will be a great addition to Cimpress. The Druck.at team's intimate understanding of Austrian web-to-print customers enables it to offer them great quality, fast delivery and a wide and deep selection of products.
"We plan to help them build on this heritage by leveraging Cimpress' scale advantages and by expanding the Druck.at product selection even further."
Druck.at chief executive Peter Kolb added: "We are very excited to join Cimpress. We anticipate benefiting from Cimpress’ global operational and supply chain advantages while maintaining the distinct Druck.at brand and focus on the needs of Austrian customers. This unique combination should allow us to improve our customer value and customer satisfaction even further."
Founded in 2001, Druck.at recorded a turnover €34m in the 12 months to 31 January 2015, up 15% year-on-year, with a net income of approximately €2m and EBITDA of approximately €3.6m.
Cimpress said it expects the deal to complete during its fiscal fourth quarter, following completion of various closing conditions, including antitrust clearance.