Tagicakibau, 28, has scored ten tries in 22 starts for London Irish in European competitions since joining the Exiles 6 years ago.
Hala'ufia's hard hitting reputation goes before him and he has amassed 21 European appearances between his time at Harlequins and London Irish.
Head coach Toby Booth, who saw his side beat double Heineken Cup champions Munster on the opening weekend of this year's competition is delighted with the extension.
"We're delighted that Sailosi and Chris have signed long term contracts with us. There is no doubt that these two players have been on the wish lists of many clubs both in the Aviva Premiership and France," he said.
"We've often spoken about this club's determination to continue compete consistently with the best of the best in this country and Europe to win silverware. Retaining the services of quality international players like Sailosi and Chris is essential to the realisation of our objectives. "
Speaking about his decision to spend the next four seasons with London Irish, Sailosi Tagicakibau said, "The environment at London Irish brings out the best in me. As an islander, family is a priority and this club is one big family. It's also important to play and share the experience with good friends and fellow countrymen like Seilala Mapusua, Elvis Seveali'i and George Stowers. We enjoy the style of rugby the club plays and want to be part of winning the trophies it deserves."
Hala'ufia said, "I've played some of the best rugby of my career since I joined London Irish. Working with Toby Booth and the coaching team has helped my game to flourish and I'm looking forward to being part of a great squad that is highly ambitious and on its road to great success."