The Provincial Growth Fund scheme was set to upgrade the network in case of damage, Infrastructure Minister Shane Jones said.
The links will run between Fox Glacier and Lake Hawea for about 240km, and from Te Anau to Milford Sound for about 120km.
He said it was part of a telecommunications infrastructure upgrade nationwide.
The fibre links will cover mobile towers totalling a combined 187km of "mobile black spots" on State Highways 6 and 94, and 21 tourism sites in both areas.
The Fox Glacier to Lake Hawea link will also provide an alternative route to existing fibres which are primarily on the East Coast of the South Island. The new link will generally follow SH6.
This link will also enable Haast township to be added to the Ultra-Fast Broadband rollout. Businesses in Milford Sound and along the route to Te Anau will also benefit from enhanced broadband and mobile services.
It is expected that the Fox-Hawea fibre link will be completed in the first half of 2022 and the Milford link by the end of 2022.
