Early Life and Role in Jewish Council
It is likely Joseph served on a local Sanhedrin, whether that be specific to Arimathea or a nearby larger town. It is then likely that he gained a reputation and eventually was selected to be on the Grand Sanhedrin. During this time he would have moved to Jerusalem. Here Joseph bought a new tomb, which had to be cut out of rock, in a garden near Golgotha. At his appointment to the Grand Sanhedrin, Joseph was in the upper class. It is not known whether or not he inherited his riches, if he achieved them as a result of being on the Sanhedrin; or both.
During his tenure on the Grand Sanhedrin he became associates with Nicodemus. It is possible that through his association with Nicodemus did Joseph of Arimathea become a Christian or vice versa. Nevertheless Joseph at one point or another was a disciple of Jesus, awaiting God's kingdom, doing so in secret in fear of the other leaders. This fear may have been for losing his position, thus his reputation, and his entire lifelong career; in addition to likely persecution and punishment.
Joseph would have been present when the Sanhedrin held a meeting concerning Jesus, lead by the Chief Priest Caiaphas in his home. In this meeting the majority of the Sanhedrin decided to persecuted and eventually execute Jesus, as he was a "threat" to the reunification of Israel and the relationship between the Jews and Rome.
Later the Sanhedrin had Jesus arrested. The Sanhedrin held a full fledged trial against Jesus, attempting to find him guilty of blasphemy by bringing forth witnesses. Despite no proper witnessing, the majority of the Sanhedrin agreed to have Jesus sentenced to death. Joseph, along with Nicodemus, discreetly disagreed. This may have been an easy task based on the large size and probably infrequency of Grand Sanhedrin meetings. He would have been present also when the Sanhedrin brought Jesus before Pilate to be crucified.
After Jesus was crucified Joseph came and asked Pilate for Jesus's body. Accompanying him was fellow believer and councilman Nicodemus. Together they purchased some linen cloth. Then Nicodemus went and took down Jesus's body from the cross and wrapped his body in linen then sprinkled some spices. He then buried Jesus in his tomb.