The 28-year-old has been with the club for over a decade having joined the academy ranks in 2003 and is all set to reach 200 hundred appearances in Saturday's Aviva Premiership clash with London Wasps.
His decision to continue his association with the Exiles comes on the back of the short-term signing of Wallaby back James O'Connor and the more long-term extensions agreed with club captain George Skivington, fly-half Ian Humphreys and England hooker David Paice and Smith is delighted to have kept hold of a player he believes personifies what London Irish are all about.
"Signing him up for the next three seasons is a massive gesture on the club's behalf and it shows how much we respect what he does on and off the park," said Smith.
"He's a great role model for all young England back-three players. We've managed to produce a lot of quality, back-three players but there's few better than Topsy Ojo.
"He's been with the club every moment of his professional career. He has gone on to play for England and he adds a lot to the group. He's a great person and a genuine London Irish legend."
Ojo himself is equally complimentary about the club as a whole, with the twice-capped England international convinced good things lie ahead for London Irish despite a frustrating start to the domestic season.
Irish lie 11th in the Premiership but are top of Pool 5 in the Amlin Challenge Cup having picked up maximum points from their first two fixtures. Victory over French giants Stade a week on Saturday would put them in control of their own destiny at the halfway mark of the pool stages and give them real hope of finally going one better than their runners up spot in the competition seven years ago.
"I'm happy to have re-signed and be part of what is set to be a really exciting next few years. We've got the new training facility coming in next season and the squad's got a good, settled feel about it, so hopefully we can really start to build and create some stuff," said Ojo.
"It's a great club and I've enjoyed every moment of being here. It was an easy decision because I'm happy here and the rugby that we play suits me down to a tee: it allows me to express myself and get my hands on the ball and that's exactly what I want.
"We've been unfortunate in the fact we haven't got the results that we have needed to cement the hard work that we've been putting in, because we've been working unbelievably hard. Anyone that has seen the last two performances against Leicester and Northampton, who are two top teams, has seen that we have pushed them really hard. And for a decision here or there on another day we'd be walking away with four points each time.
"But you need somewhere to start off with, and, from where we have been, we can take confidence and belief that we're playing some really good stuff and are in a much better place. So we need to keep at it and keep believing and we'll kick on."