Short answer: no, the Roman soldier who pierced Jesus with a spear was probably not named Longinus, although there is a tradition that not only names him but provides a colorful history of his further exploits. The long answer follows:
First, here is the biblical account of the piercing of Jesus’ side, which says nothing about a man named Longinus: “Now it was the day of Preparation, and the next day was to be a special Sabbath. Because the Jewish leaders did not want the bodies left on the crosses during the Sabbath, they asked Pilate to have the legs broken and the bodies taken down. The soldiers therefore came and broke the legs of the first man who had been crucified with Jesus, and then those of the other. But when they came to Jesus and found that he was already dead, they did not break his legs. Instead, one of the soldiers pierced Jesus’ side with a spear, bringing a sudden flow of blood and water. The man who saw it has given testimony, and his testimony is true. He knows that he tells the truth, and he testifies so that you also may believe. These things happened so that the scripture would be fulfilled: ‘Not one of his bones will be broken,’ and, as another scripture says, ‘They will look on the one they have pierced’” (John 19:31–37; cf. Numbers 9:12; Psalm 34:20; Zechariah 12:10).
From Scripture, here is what we know: soldiers (at least two) were tasked with breaking the legs of the men on the crosses to hasten death. The legs of the two thieves crucified with Jesus were broken, but the soldiers did not break Jesus’ legs because they found He was already dead. One of the (unnamed) soldiers pierced Jesus’ side with a spear, and blood and water flowed out. John was an eyewitness to these events, and verifies the truth of the account.
The soldier who pierced Jesus’ side is named Longinus in the pseudepigraphal Gospel of Nicodemus. Here are the details that the legend of Longinus adds to the biblical story: a centurion from Cappadocia named Gaius Cassius Longinus, who was nearly blind, was assigned to crucify Jesus. Upon Jesus’ death, Longinus took his spear and pierced Jesus’ side; some of the blood and water that came out splashed into Longinus’s eyes, curing his eye condition instantly. Then Longinus said, “Surely this man was the Son of God!” Later, Longinus was told to guard the tomb of Jesus, and he witnessed the resurrection of Christ. When the Jewish leaders attempted to bribe him to lie about what he had seen, Longinus refused. He then quit the military, became a Christian, and decided to live as a monk (even though there were no monasteries at the time). According to the legend, the early Christians obtained the spear that Longinus had used to pierce the body of Christ, and they kept it safe, revering it as a miracle-working holy object.
According to the legend, Longinus was eventually imprisoned and martyred by beheading. Various stories concerning his severed head have circulated, but they all involve someone being healed of blindness by either touching the head or having some of Longinus’s blood splash into their eyes.
Meanwhile, the spear that Longinus supposedly used was called the Holy Lance or the Spear of Destiny, and various legends sprang up concerning it, as well. One is that whoever holds the spear cannot be defeated in battle and can therefore rule the world. Several objects exist that are touted as the original spear of Longinus.
There’s a theory of how the name Longinus came to be attached to the soldier with the spear who pierced Jesus’ side. There is a historical figure named Gaius Cassius Longinus who was a Roman quaestor in the time before Christ. The historical Longinus (usually referred to as “Cassius”) was instrumental in the murder of Julius Caesar in 44 BC. It is possible that the early Christians called the soldier who pierced Jesus’ side “Longinus” as a reference to the murderer—Longinus thus could have been simply an antonomasia meaning “assassin.” (An antonomasia is a figure of speech using a person’s name as a metaphor to emphasize a particular trait.)
The Longinus of legend is venerated as a saint in the Roman Catholic Church and the Eastern Orthodox Church. The legend of Longinus, accepted as fact by so many people, is an example of mystical literature being given equal footing as the Bible. The adoration of the Holy Lance and other relics by people who attribute to them supernatural powers is a sad example of how superstition has infiltrated the church.