Howard, who has a family pharmacy business in Australia, had initially intended to quit last term before agreeing a new deal for the current campaign.
But he announced yesterday that "for family and business reasons, this will be my last year" and he will return Down Under in the summer.
Tom said: "We were delighted last year when Pat agreed to stay for another year, but we always knew it was his intention to return home at the end of this season.
"Pat has done a fantastic job for the club, initially as a player and then as backs coach and head coach. He has brought about a number of changes which have enabled us to move forward and Tigers are now in a very strong position."
Club officials are likely to mount a global search for Howard's successor, with current Springboks coach Jake White already being touted as a possible candidate.
Tom added: "We have identified a number of potential candidates as his replacement and Pat has been involved in that process, which will continue."
Howard succeeded current England forwards coach John Wells in charge at Leicester in 2005 - having enjoyed a three-season stint as a player, which included helping Tigers to lift the 2001 European title with victory over Stade Francais.
Leicester are currently second in the Premiership and on course to reach this season's European Cup quarter-finals. They have also reached the Anglo-Welsh Cup semi-finals and will play Sale Sharks in Cardiff next March.