Ordained in the Episcopal Church, he is canon theologian in the Diocese of Western Kansas, but Null maintains close ties to the Anglican realignment movement as a theological adviser to the Anglican Church in North America's Diocese of the Carolinas.

Null was born in Birmingham, Alabama, and raised in Salina, Kansas, where he grew up attending Christ Cathedral.

According to a reviewer in The Journal of Theological Studies, Null explores Cranmer's "decisive shift towards an Augustinian reading of Paul and a Lutheran understanding of justification" following a 1532 visit to Nuremberg, and Cranmer's arrival by 1537 at a theology of justification as imputed righteousness with "our assurance of salvation resting entirely on the promise of God and in our election.

[7] Through Cranmer's reshaping of soteriology, Null argues, the archbishop sought to "emphasise the generous and unreserved love God had for humankind.

thorough and penetrating in its analysis of sources, impressively conversant with the vocabulary and issues of late scholasticism, and persuasive in its picture of Cranmer's theological development.

"[7] Reviewers also praised Null's use of "little used Latin works" by Cranmer: the Great Commonplaces, De Sacramentis and the Croydon Commentary.

Thus, in its call to view the books of the Bible as "vehicles of the Spirit's work in energising the Church in its mission and shaping it in the holiness of new creation," the Windsor Report—which recommended a moratorium on the consecration of actively LGBT bishops and on blessings of same-sex unions—"has, in fact, repristinated for our day a fundamental principle of historic Anglicanism.

He was one of the authors of the Jerusalem Declaration adopted at the 2008 Global Anglican Future Conference and a keynote speaker at the 2023 GAFCON in Kigali.

[11][12] He is a theological adviser to the Global Fellowship of Confessing Anglicans and the ACNA's Diocese of the Carolinas, where he is also a senior research fellow at the Ridley Institute, the adult education program of St. Andrew's Church.

[2] Null was appointed canon theologian in the Diocese of Western Kansas in 2005, although he has spent most of his time based in Europe for his theological and historical research.

"[14] In February 2025, Null was elected the second Anglican bishop of North Africa, to succeed Anthony Ball.