The change pointed to an upgrading in industrial structure, said Ma Jiantang, director of the NBS.
The second-placed sector, industry, took about 43.9 percent of the GDP.
China's economy grew 7.7 percent in 2013 from a year earlier, to 56.9 trillion Yuan ($9.3 trillion). The growth was the same as in 2012, overshooting the government target of 7.5 percent.
The agricultural sector, or the primary sector, climbed 4 percent year on year to 5.7 trillion Yuan, the industrial sector rose 7.8 percent to 25.0 trillion Yuan and the service sector expanded 8.3 percent to 26.2 trillion Yuan, Ma said.
The service sector's outstripping of the industrial sector indicates "China's economy and society have entered a new phase," said Niu Li, an expert with the State Information Center.
According to Niu, this is in line with China's general economic growth and pattern of industrial upgrading.
New reforms in the country should focus on the service sector, especially finance, shipping and logistics, he added.
Zhang Liqun, an analyst with the Development Research Center of the State Council, said the service sector has huge capacity to absorb labor, while expending relatively little energy.
Though the improving ratio of the service sector against the economy is a trend that will continue in future, it should not replace efforts to transform and upgrade the manufacturing sector, Zhang said.
At the end of 2012, China issued its 12th five-year plan for the service sector. It aimed to raise both the proportion of GDP accounted for by the service sector and the ratio of service sector employment in the country's total employment by 4 percentage points in 2015 from 2010.