Seyyed was found guilty by Gothenburg District Court of instigating attempted murder and two counts of instigating devastation endangering the public.
Four other Bandidos members received shorter sentences for their involvement in the attacks on two cars in Gothenburg on September 19th and 20th 2006.
In both cases, hand grenades were detonated when the owners of the vehicles put their cars in reverse.
In the first incident, a taxi driver was targeted as part of a suspected revenge attack after he had testified against Seyyed, Expressen reports.
The following day, the security manager from a popular Gothenburg nightspot was fortunate to escape with only minor injuries when his petrol tank caught fire in the blast and his car exploded.
The prosecution was assisted in the case by a 23-year-old former member of Bandidos "supporter group", X-team. The new witness came forward with incriminating evidence against Meyyed during the summer, Expressen reports.
The witness has lived under state protection at a secret address ever since his apartment was vandalized when he testified in an earlier case to being assaulted by Meyyed. The 23-year-old's testimony led to a conviction in March last year and a two and a half year prison sentence for the Bandidos leader.