The deal, which had been well flagged to the market, comes as Toshiba's hopes of growing profits in its nuclear power division are being overshadowed by the crisis at Japan's tsunami-hit Fukushima reactor, and utilities around the world focus on smart grids as a means of saving energy and cutting carbon emissions.
The smart grid market is expected to grow six-fold to 5.8 trillion yen US $70.9 billion over the next decade, Toshiba said.
"Quality comes at a price," said Macquarie Equities Research analyst Damian Thong.
"I think it would be near impossible for Toshiba to build a business like this organically."
Smart grids are designed to accommodate a range of generation options, including renewables, and to provide customers and utilities with more real time information, enabling them to manage usage and supply more efficiently.
Landis+Gyr is a maker of both smart meter hardware and communication modules, key components of smart grids. It competes with companies such as Itron Inc and EnerNoc Inc.
The Swiss firm's earnings before interest, taxes, depreciation and amortization came to $215 million dollars in the year to March 2011, on revenue of $1.59 billion.
Credit Suisse and Lazard Ltd advised Landis+Gyr on the sale.
Toshiba declined to comment on how it would finance the deal, but the Japanese firm will likely have enough cash on hand to cover most of the cost, depending on the size of Landis+Gyr's debts, Macquarie's Thong said.
Toshiba said it had yet to determine the impact of the acquisition on its business performance in the year to March 2012.
Media reports had said the Japanese conglomerate might team up with other firms in the buy-out, but Toshiba said it had agreed to acquire the whole firm.
Landis+Gyr, founded in 1896, is owned by several equity funds and individual investors, after going through a series of different owners including Kohlberg Kravis Roberts & Co and Siemens in the 1990s.
The firm boasts more than 8,000 utility customers globally, and its 5,000 employees operate in more than 30 countries. There are no plans for job reductions following the deal, Landis+Gyr said.
In January it was chosen to supply 10,000 smart meters to the State Grid Corporation of China as part of the construction of the world's largest smart grid.
The Toshiba takeover, which is subject to regulatory approval, is expected to close in the third calendar quarter of this year, Landis+Gyr said.