Smith was pleased to have secured the services of a player with a strong pedigree.
"I've been after Chad for a while so to get his signature now is important for me and for the squad," he said.
"It's a massive coup for WaiBOP United to have a player of Chad's standing sign on.
"It's recognition of what we're doing here and where this team is heading. Chad is a strong, aggressive leader, a quality player and a top lad. He'll bring so much to our playing group."
Coombes has had a storied ASB Premiership career with both Auckland City and Waitakere United.
He signed for Auckland City ahead of the 2005/06 season and won four ASB Premiership titles, three OFC Club Championships and travelled to the Fifa Club World Cup three times.
With Waitakere United, where he played the last two seasons, Coombes picked up one further ASB Premiership title.