Answer: The Bible does not have a list labeled 'the seven deadly sins.' This list was likely the creation of a Catholic Church monk around the 4th century A.D. which was retained by the church's theologians starting in the Middle Ages (1913 Catholic Encyclopedia article on Sin). Catholics officially teach that there are at least seven "capital sins" that humans can indulge in.
The Catholic list of seven capital (deadly) sins is not a collection of the worst offenses man can commit. It is a list of what they consider are the worst attitudes that are the foundation and starting point for all other disobedience to the Eternal. The most common list of seven attitudes they consider deadly are wrath, greed, lust, pride, envy, sloth and gluttony.
The nearest thing in the Old Testament to a list of seven sins considered deadly is in the sixth chapter of the book of Proverbs.
Solomon writes that God hates those who is full of pride, a liar, a murderer of those who are innocent, a person who devises ways to do evil and those who are eager to do wrong. He also hates those who bear false testimony against another person and those who seek to pull people apart through sowing seeds of contention (Proverbs 6:16 - 19).
The New Testament has at least two lists that delineate several, but not exactly seven, major sins.
The first list is found in 1Corinthians 6:9 - 10 where the apostle Paul states that adulterers, thieves, drunkards, extortioners, the covetous and so on will not receive eternal life. The second list of sins, found in Galatians 5:19 - 21, states that those who practice fornication, idolatry, sorcery, spreading dissensions and heresies, contentious behavior and still others will not be in God's kingdom!
Ultimately, the Bible teaches that sin, which it defines as the transgression of any of the laws of God, if unrepented of will bring the penalty of eternal death. The Bible refers to knowingly and willfully rebelling against God's way as the unpardonable sin, which, given its penalty, can certainly be considered deadly! The apostle John reveals the standard by which we can know whether or not we are sinning before God.
And by this standard we know that we know Him: if we keep His commandments. The one who says, "I know Him," and does not keep His commandments, is a liar, and the truth is not in him (1John 2:3 - 4).
The book of Galatians records (as well as many other books) that all mankind, from the greatest to the least, sins. The book of Romans further specifies that those who do so must pay with their lives (Galatians 3:22, Romans 6:23)!
Thankfully, God has provided a way for us to be forgiven of all sins, "deadly" or not, through the unselfish sacrifice of Christ (Romans 5:8). He does not forgive us only seven times (the number Peter thought was the upper limit, see Matthew 18:21) but is gracious and merciful to overlook our trespasses as many times as it takes (verses 21 - 22)!