More than 64 percent cast ballots in favour of the project to connect Zurich's Alstetten neighhourhood, northwest of the city centre, with Killwangen in Aargau, according to figures from the canton of Zurich.
The majority approved the cantonal government spending 510.3 million francs for the LRT, plus an additional 136.3 million francs for related road works along the corridor.
The canton of Aargau's government has already approved spending 180.5 million francs for the project.
The line, set to be completed by 2022, will serve one of the fastest growing parts of Switzerland with 27 stations.
The first section of the line, set to be completed by 2019, will link Zurich-Altstetten with the municipality of Schlieren.
The federal government has agreed to cover 35 percent of the costs of the Limmatalbahn's first section and is expected to follow suit for the second section.
The LRT is designed to limit urban sprawl by encouraging the densification of housing close to rail stations, while relieving congestion on the region's roads and S-bahn train lines.