Cooper and Hatfield will add an experienced edge to the young Thunder squad as both wingers have played and trialled overseas.
Cooper spent two and a half years in Holland with VVV Venlo. His first season with the club was in the Dutch Eredivisie, Holland's top soccer division, before they were relegated to the second division.
He has also spent time in the A-League with the Newcastle Jets before joining the Thunder from Manly in the New South Wales NPL.
Cooper said he was looking to share his experience with the Thunder.
"I'm looking forward to the challenge," he said.
"I want to help push the players and the team forward and in turn I hope they will push me forward as well."
The 23-year-old, who plays on either wing, said he like to pressure his opponents with his direct play.
"I like to try and get in behind the defence and create opportunities," Cooper said.
"I like that direct style of play, taking on my defender, before getting that cross in."
Hatfield spent time in England trialling for Premier League side Stoke City and third tier side Southend United FC.
The 23-year-old, who can also play on either wing, joins the Thunder from NSW NPL 1 champions Fraser Park.
"I'm very excited by this move - it just seems right for me," he said.
"They're a young side but I don't think a lack of experience matters.
"It shows the club is looking to the future, trying to develop. As long the attitude that's what matters."
Hatfield shared a similar philosophy to Cooper.
"I think my speed, dribbling and direct play are my strongest assets," he said.
"I'm always looking to make crosses and I think I'm very effective in one-on-one situations."
Thunder media manager Laurie Passante said the club was excited by the deal.
"We have a number of key positions we wanted to fill - this is part of that plan," he said.
"Our focus has always been on local player development and this is part of that process.
"Signing Chris and Travis gives our younger players to watch, learn and develop."