The NRL expects Ben Barba to serve his 12-match illicit drug before debuting in the Super League after he signed with St Helens.

It would rule the former Cronulla star out until at least August, near the end of the English season.

Fullback Barba has secured a two-and-a-half year deal with the Saints after being released by French rugby union club Toulon just three months into a two-and-half year agreement there.

St Helens indicated they may appeal against having to enforce his NRL ban for a second positive test to cocaine in Australia.

But an NRL spokesperson told AAP the two countries have a reciprocal acknowledgement of bans and England’s governing body Rugby Football League had confirmed it would honour that.

St Helens beat Super League rivals to the NRL premiership-winner’s signature on Wednesday.

The 27-year-old copped the illicit drug ban after testing positive following the Sharks’ grand final victory last season, prompting him to head overseas.

Barba, who won the Dally M award in 2012, is set to miss the last nine matches of the Super League regular season and the first three fixtures of the Super 8s.

“I feel very privileged to be joining such a historic rugby league club as St Helens,” Barba said.

“I was able to meet up with some of the players and key people from the club at the Magic Weekend and know they are a great set of people. The fans also showed me just how passionate they are.

“I wanted to make an early decision so that I can get my family settled in England and kids enrolled at school.”

Saints coach Justin Holbrook said Barba was world-class.

“Everyone in the team will benefit from him joining us,” Holbrook said.

“It is not often that players of his calibre become available and the club has pulled out all the stops to fight off competition from both rugby codes around the world.”