The pipeline will begin to transport natural gas by mid December, which will supply up to 20% of the UK's gas needs.
Wicks opened the final section, between Felindre and Brecon, yesterday and welcomed the new LPG deliveries, "once imports into Milford Haven start next year, and it will also help to secure Wales' energy supply for many years to come.
"In the past, Wales's gas has been piped through England and Scotland. Now, for the first time, Wales is at the front end of the UK's gas supply system.
"The new pipeline will also allow further economic development in South Wales, with new power stations and industrial expansion possible. Thanks to the pipeline there is also the potential to meet rising demand, and connect more homes to the gas distribution network," he said.
The project has been difficult to complete, snaking around the Welsh countryside it had to pass beneath several roads and rivers without disruption.
Some farmers and other local landowners had strong objections to the project. National Grid Executive Director of transmission, Nick Winser said: "We have worked hard to balance issues such as the concerns of landowners, topographical constraints, environmental effects, and construction difficulties.
"We have worked closely with both the statutory bodies, local councils and communities to minimise the temporary effects of construction on the environment and local people."