Seaports and cities are internally linked, and the port can have a strong influence on the city, especially in the environmental aspect. Port authorities around the world are striving for greener forms of port management to adapt to state policy and to increase their economic and environmental competitiveness. The introduction of the concept of sustainable development in the port can stimulate the creation of green cities. This paper uses a case study to analyze the sustainable development in the Twin Port of Bremen. The aim is to distinguish the green port’s impacts that can stimulate the development of the green city concept. It is shown that the port development stimulates GDP growth, increases employment, urban infrastructure development, and the overall enrichment of port cities. Using the presented analysis of the green port, the most important affecting factors are proposed.