Defence Minister Tony Killeen said 440 troops would be sent to the country before next summer to serve under the UN.
The Cabinet has approved the proposal and Mr Killeen will seek the backing of the Dáil in the coming months.
“It is vitally important for Ireland to maintain a level of commitment to international peacekeeping operations and the obligations it has assumed through its membership of the UN,” he said. “Overseas operations contribute greatly also to the professional development of the Defence Forces.”
Army chiefs had been considering options for the international deployment of troops since the unexpected withdrawal from Chad earlier this year.
Irish soldiers served in the United Nations Interim Force in Lebanon (UNIFIL) from its establishment in 1978 until 2001. Another contingent was deployed for one year in 2006 after an escalation in hostilities.
Chief of staff Lieutenant General Sean McCann said he was delighted with the planned deployment.
“We have a long and proud tradition of service in the Lebanon and we look forward to using our skills and our experience to make a substantial contribution to the peace and security of the region.”
The soldiers will operate in an area of around 140sq km extending from Tibnin to the border with Israel.
A total of 47 Irish troops lost their lives during peacekeeping missions in Lebanon since 1978.
The Department of Defence said the mission would cost taxpayers €5 million next year, falling to around €3m in 2012.