Fire service staff will help enforce a new default speed limit, which comes into force in September.
The country will become the first nation in the UK to introduce a default 20mph limit on restricted roads from 17 September.
The fire service says it will only be providing road safety advice to motorists exceeding the limits, who will have an opportunity to watch a roadside “educational video” rather than face prosecution.
However, the videos are only offered to drivers who do not drive “excessively over” the speed limit.
Police will stop drivers exceeding the limits and those speeding will be fined.
The Welsh Conservatives, the largest opposition party in the Senedd, have called the default limit, which has already been trialled in some parts of the country, a “madcap” policy.
As well as the fire service and police, the government’s awareness campaign will involve local authorities, community groups and Go Safe – Wales’ road casualty reduction partnership.
South Wales Fire and Rescue Service group manager Richie Smart said the service was “pleased” to support the rollout.
“Our firefighters see the devastating impacts that road traffic collisions, including those in built up areas where people and vehicles mix closely, can have,” he said.
“We are therefore pleased to support our partners to raise awareness of the importance of speed limits to keep everyone safe.”
Superintendent Leanne Brustad, from Gwent Police, said “engagement, education, and enforcement plays a huge part”.
“We will continue to work closely with our partners to educate drivers as much as possible as the new speed limit comes into force and help deliver all of the benefits of this policy,” she added.
The Welsh Conservatives’ shadow transport minister, Natasha Asghar, said the move was “spreading a stretched public service even thinner”.
“The priorities of our fire service should not include catching motorists speeding,” she said.
“The Labour government are showing that this foolish policy is not about safety or the environment, as they have claimed, but using public services to catch out motorists and collect money in fines.”
Climate change minister, Julie James, has previously said the policy would make streets and communities “safer”.
“We know this move won’t be easy – it’s as much about changing hearts and minds as it is about enforcement – but over time 20mph will become the norm, just like the restrictions we’ve introduced before on carrier bag charges and organ donation,” she said.