Two years after the trial began, the regional high court in the southwestern city of Stuttgart handed Ata Abdoulaziz Rashid a 10-year sentence, Mazen Ali Hussein seven-and-a-half years in prison and Rafik Mohamad Yousef eight years.
The three were convicted of belonging to a foreign terrorist organization - Iraqi militant group Ansar al-Islam - and attempted conspiracy to commit murder.
The court found that they had plotted to assassinate Allawi in a plan hatched only days before his brief trip to Berlin in December 2004.
Presiding judge Christine Rebsam-Bender said police had been tracking Rashid, now 34, since October 2003.
"The key evidence came from surveillance of Rashid's telephone calls and emails," she said.
Defence attorneys for the three said they would appeal the verdict.
Rebsam-Bender said the defendants' frequent legal challenges had led the trial to drag on for more than two years. She also cited frequent outbursts by Yousef, 33, including an attack on a prison guard that broke the officer's rib.
"He was hot-tempered and aggressive," she said.
"Because they are Nazis!" Yousef shouted to the judge.
Authorities insist they foiled the planned attack but conceded before the start of the trial in June 2006 that they knew too little of the plan to charge the defendants with attempted murder.
Ansar al-Islam, a predominantly Kurdish group, is believed to have links to the slain extremist Abu Musab al-Zarqawi's al-Qaida organization in Iraq.
Intelligence services estimate it has about 100 members in Germany connected to a wider network of supporters across western Europe.
The defendants are the latest suspects being tried under a law adopted in the wake of the September 11, 2001 attacks on the United States that allows Germany to jail members of foreign terror groups for up to 10 years. The law had previously covered only domestic terror organizations.
The men were netted in three different cities - Augsburg, Berlin and
Stuttgart - when police mounted early morning raids the day of the planned attack.
Rashid, who was arrested in Stuttgart, is believed to have been the ringleader and to have been informed of other attacks planned by Ansar al-Islam.
The court found that he collected funds and recruited potential suicide bombers for the group, which has claimed responsibility for a series of bloody attacks on US troops and aid workers.
Authorities found that Hussein, 27, was a close accomplice of Rashid's who also drummed up funding for Ansar al-Islam in Germany.
The court estimated Rashid had raised about €45,000, some €20,000 of which was funnelled to Ansar al-Islam in Iraq to fund attacks and pay stipends to families of suicide bombers.
Hussein told the court in September 2006 that the intention was not to kill the Iraqi leader but to "teach him a lesson". He conceded having made telephone calls which contained coded messages about the plot.
Yousef is believed to have approached Hussein just five days before Allawi's arrival in Germany seeking support for his idea to kill the prime minister.
Germany's former federal prosecutor, Kay Nehm, said at the time that inside sources had tipped off the group about Allawi's movements.
At least two events on Allawi's schedule were called off for security reasons, including a meeting with Iraqi exiles in Berlin which police believe the alleged plotters had hoped to target.