On September 25, 1929, Westminster Theological Seminary opened in the Witherspoon building in Philadelphia, with an enrollment of fifty students.
In his opening address, "Westminster Theological Seminary: Its Purpose and Plan," J. Gresham Machen set forth the school as the successor to Princeton Seminary, which had been recently reorganized to include modernists on its Board:
[T]hough Princeton is dead, the noble tradition of Princeton is alive. Westminster Seminary will endeavor by God's grace to continue that tradition unimpaired; it will endeavor, not on a foundation of equivocation and compromise, but on an honest foundation of devotion to God's Word, to maintain the same principles that the old Princeton maintained. We believe, first, that the Christian religion, as set forth in the Confession of Faith of the Presbyterian Church, is true; we believe, second, that the Christian religion welcomes and is capable of scholarly defense; and we believe, third, that the Christian religion should be proclaimed without fear or favor, and in clear opposition to whatever opposes it, whether from within or without the church, as the only way of salvation for lost mankind. On that platform, brethren, we stand. Pray that we may be enabled by God's grace to stand firm. Pray that the students who go forth from Westminster Seminary may know Christ as their own Savior and may proclaim to others the gospel of his love.
Though an independent school, Westminster Seminary proved crucial to the founding and development of the Orthodox Presbyterian Church. Most of the church's ministers have graduated from Westminster, and its founding faculty, all of whom were ministerial members in the OPC, were active and prominent churchmen. In the words of Charles Dennison, the two institutions developed "one of the most amazing relationships in Presbyterian history.