Portsmouth have made Kanu their fifth summer signing after the striker agreed to a one-year-deal at Fratton Park.
The 31-year-old Nigerian will bolster the Pompey strikeforce after leaving West Brom in the summer following their relegation from the Barclays Premiership.
Kanu was part of Arsenal's double-winning side of 2001-02 and gained another Premier League medal in 2004, contributing 37 goals during his stay at Highbury.
It brings some relief for Pompey boss Harry Redknapp, who earlier today revealed: 'It is the smallest squad I've ever had at the start of a season.
'We are still at least four players short and a run of injuries would be very bad news for us.
'We've tried for a long list of big signings and the owner has been ready to put up the money for them.
'But other clubs just don't want to sell their good players and it has been a frustrating time.
'But we still have two weeks (before the transfer deadline) to put that right and we are still looking to do that. There is no way we can afford to wait until January (the next deadline).''
The manager has recruited just four other players this summer -- Chelsea right-back Glen Johnson, former Arsenal centre-half Sol Campbell, ex-Blackburn and Wigan midfielder David Thompson, and former Manchester City goalkeeper David James.
Redknapp was snubbed in big-money bids for stars like Jermain Defoe (Tottenham), Stilian Petrov (Celtic), Gareth Barry (Aston Villa), Curtis Davies (West Brom), Nicolas Anelka (Fenerbahce), Ryan Nelsen (Blackburn) and Sylvain Distin (Manchester City).
As he prepares his squad for Saturday's Barclays Premiership opener against Blackburn, he admitted: 'It has just gone crazy in the transfer market.
'No disrespect but Birmingham have had to pay £4million for Gary McSheffrey and some clubs won't sell at any price.'
Redknapp, 59, is so short of resources for the clash with Mark Hughes' Rovers that he has to choose between fitness doubts Kanu and Zimbabwe striker Benjani Mwaruwari -- the club's record £4.1million signing in January -- to partner Svetoslav Todorov in attack on Saturday.
Kanu has not played a competitive match since relegated Albion discarded him at the end of last season and Benjani has a thigh strain following his recovery from a summer knee operation.
Last season's front-man Lomana LuaLua is now being labelled a 'long-term' absentee after damaging an ankle in a pre-season game.
And Redknapp will have 17-year-old untried youth goalkeeper Nick Jordan on the bench against Blackburn with Kiely (thigh) and Ashdown (broken thumb) still weeks away from recovery.
Meanwhile Pompey have pulled out of a deal for £1.6million Peru left-back Juan Vargas who has been training with the club but could still go for £7million rated Portuguese midfielder Manuel Fernandes who is trying to prove his fitness after a groin injury that has failed two medical examinations.
Redknapp said: 'It is a day-to-day thing with him but he seems to be getting there and we will see what is situation is in a couple of weeks.
'For now, though, we just have to show the spirit and fight we had in the second half of last season and hope for three points from the first match.
'It has been a frustrating summer but we are still in there trying and I couldn't ask for more support from the owners.'