US-based BTP and Aecom have won the contract.
The work involves installing an integrated monitoring system based on remote monitoring sensors and basic equipment for border security along the 250 kilometre barrier built in 2015 between Ras Jedir and Dhehiba. Tunisian security forces will also be trained in its use.
The US committed to tripling its military aid to Tunisia in 2015, from around $60m in 2014.
The border barrier, including fences, trenches and sand walls along the desert border between Tunisia and Libya, was begun following a terrorist attack on tourists in the coastal resort of Sousse.
The gunman is thought to have trained and planned his attack in war-torn Libya.
More recently, more than 50 people were killed in an attack on the border town of Ben Guerdane.
The porous border has long been a focus of smuggling, and several arms caches have been discovered, raising concerns that violence in Libya will destabilise Tunisia.