The 32-year-old, who plays Sheffield Shield cricket in Australia for Victoria, had one season at Glamorgan in 2000 and replaces compatriot Jimmy Maher.
Maher, who has also provided occasional wicketkeeping back-up to Adam Gilchrist, was due to link up with Queensland team-mate and Australia fast-medium bowler Michael Kasprowicz at Glamorgan but cannot now make the start of the English season.
Elliott, 32, who has also played County cricket for Yorkshire, is expected ahead of Glamorgan's opening County Championship match against Derbyshire in April.
Glamorgan chief executive Mike Fatkin said, "Jimmy Maher was due to return to Glamorgan this summer but he informed us a few weeks ago that he was unlikely to be available for the opening games of the season for personal reasons.
"We understand his reasons but he in turn appreciates the importance which our captain Robert Croft and First XI coach John Derrick attach to having our overseas players available for the start of the season.
"We had to move quickly to find a suitable replacement and we are delighted that Matthew Elliott has agreed to rejoin us this summer. "We know Matthew well from his time at Glamorgan in 2000, when he helped the team reach its first major Lord's final in 23 years."
Elliott has scored more than 1,000 runs for Victoria in first-class cricket during the current Australian season, including six hundreds.
In his previous season with Glamorgan, he passed the 1,000-run mark in 12 County Championship matches while he was named Man of the Match in Yorkshire's 2002 One-day Trophy final win at Lord's for an unbeaten 128.
Elliott, who still has ambitions to play international cricket again, played the last of his 20 Tests against the West Indies at Bridgetown, Barbados in the 1998-99 season.
His Test record of 1,171 runs at an average of just over 35 with three hundreds was respectable but such has been the strength of Australia's top-order batting in recent years that Elliott has not had a look-in since with his compatriots dominating both five and One-day forms of the game.