Farrell is set to be unveiled at a press conference at Vicarage Road on Thursday afternoon.

The RFU, who have identified Farrell as a potential England player, agreed a deal with Farrells Super League club, Wigan, earlier this month.

They had since been in negotiations to place the 29-year-old with a Premiership club.

The move is a gamble by the RFU, who will jointly fund the players salary along with Saracens.

Farrell is currently recovering from knee surgery after breaking down during Wigans pre-season training camp in the United States.

There is also uncertainty over which position Farrell, predominantly a loose forward in rugby league, will play in the 15-man code.

However, it is his leadership and goalkicking qualities that have appealed to the RFU, who have previously dipped into the rugby league ranks to sign Jason Robinson and Henry Paul.

Farrell is an icon in rugby league and enjoyed one of his finest seasons last year. He led Wigan to the latter stages of the Super League play-offs and earned the prestigious Man of Steel award for the second time in his career.

He was awarded the OBE for services to the sport in the New Years Honours.

He made his debut for hometown Wigan at the age of 16 and went on to win 34 Great Britain caps. He has led them in their last 29 Tests matches, a run stretching back to 1996.

Farrell has little rugby union experience, other than Wigans cross-code match against Bath and their Middlesex Sevens appearance in 1996.

The RFUs interest in Farrell first emerged a month ago but with the player injured a deal was not been rushed through.