The word “saint,” as you use it here, refers to those whose lives have been recognized by the Church as having marked them as assuredly being in Heaven. It is certainly scriptural that there are “saints” in heaven, since that is where the blessed go when they leave this life. In the New Testament, the word is applied both to the living and to those who have “fallen asleep.”
The practice of acknowledging that our brethren had assuredly been received into heaven developed in apostolic times. In the Acts, Chapter 7, the martyrdom of Stephen gives a view of what the Apostolic Church understood to be a certainty of having been received in heaven:
55] But he [Stephen], full of the Holy Spirit, gazed into heaven and saw the glory of God, and Jesus standing at the right hand of God;
56] and he said, “Behold, I see the heavens opened, and the Son of man standing at the right hand of God.” . . .
58] Then they cast him out of the city and stoned him; . . .
59] And as they were stoning Stephen, he prayed, "Lord Jesus, receive my spirit."
60] And he knelt down and cried with a loud voice, “Lord, do not hold this sin against them.” And when he had said this, he fell asleep.
The martyrs were recognized as saints by the second century. The martyrdom of Polycarp (A.D. 155) remains one of the most moving and beautiful accounts in all of Christian literature. The commemoration of the anniversary of his martyrdom began immediately:
“We have at last gathered his bones, which are dearer to us than priceless gems and purer than gold, and laid them to rest where it was befitting they should lie. And if it be possible for us to assemble again, may God grant us to celebrate the birthday of his martyrdom with gladness, thus to recall the memory of those who fought in the glorious combat, and to teach and strengthen by his example, those who shall come after us.”
Criteria for sainthood are given by God himself via the commandments, the beatitudes, and the pattern of Jesus’ life. It was universally held by the apostolic and sub-apostolic Church that martyrdom for the faith assured salvation – although the Church reserved the right of approving such honor, even for martyrs (who were called vindicati), before a saint could be publicly recognized. Not until the 4th century were non-martyrs recognized as worthy of veneration.
Between the 7th and 12th centuries saints were recognized locally in churches and councils, with papal recognition gradually becoming more important in the interest of certainty and of preventing abuses. It was not until 1634 that the right of canonizaton was reserved exclusively to the Holy See.
Today the process is cautious, lengthy and complex. It should be noted that the Church does not “create” saints. God does. The Church merely recognizes them.
So, yes, saints are biblical, since the Bible tells us that the goal of our life is to be with God in eternity, and that is where we know the canonized saints are.