The firm said the sale of TGGT is part of its renewed focus on exploration, production and liquid natural gas (LNG), which has been prompted by a fall in the price of US gas prices in recent years as more fuel from unconventional sources such as shale enter the market.
Azure Midstream Energy is buying out both BG and its partner, EXCO Resources, for a total of $910m including debt settlements.
As part of the deal, BG will end up with a four per cent stake in Azure, worth $17m.
TGGT operates more than 1,000 miles of pipelines to move gas from Louisiana and Texas sources to larger, interstate supply lines.
The disposal is the latest in a line of sell-offs by BG, following its $176m sale of a Chilean LNG terminal last month and the $422m deal to get rid of gas distributor Gujarat Gas Company over the summer.
The TGGT deal is expected to close at the end of the year, subject to relevant regulatory approvals.