The 6.4km seven-station underground line operates an extension of the north-south Tamsui Line, running east from Chiang Kai-shek Memorial Hall to serve Dongmen, Daan Forest Park, Taipei 101/World Trade Center, and Xiangshan.
Taiwan Rapid Transit Corporation (TRTC) says aesthetics were a key consideration in the design of the stations, and each of the five-stations has a theme which reflects the characteristics of the surrounding area.
The opening of the automated line is expected to take ridership on the TRTC network to more than 1.8 million passengers per day.
TRTC is celebrating the opening of the line by offering free travel between Chiang Kai-shek Memorial Hall and Xiangshan, while holders of the city's EasyCard will be entitled to a 30% discount for journeys between Xinyi Line stations and selected stations elsewhere on the network.
A further 1.6km two-station extension from Xiangshan to Zhongpo is planned.