[4] Sinclair entered Cranmer Hall, Durham, an Evangelical Anglican theological college, to train for the ministry.

Its vision is to uphold traditional biblical teaching on sexual relationships and gender and to do so with "understanding and compassion, so that Christians who struggle with same-sex attractions or gender identity gain increasing acceptance, wholeness and maturity in faith within their local church.

"[citation needed] Sinclair was one of the bishops selected to be a member of the Church of England working group on human sexuality which in 2013 produced the Pilling Report.

Two essays are appended to the Report: One, by Sinclair, epitomises a conservative understanding of the biblical texts; the other by David Runcorn argues a scriptural case for a more inclusive ethic.

The report, by way of explanation for the essays, states: "We include these two contributions, not because they sum up the whole range of scriptural scholarship on this subject — they emphatically do not — but because they epitomise the way in which study of the same sources can lead to very different conclusions."

[13] In July 2024, he was commissioned by the Church of England Evangelical Council as an "overseer" to provided alternative spiritual oversight (not to be confused with the Church of England's official alternative episcopal oversight) to evangelical clergy and parishes in the Church of England who maintain traditional teaching on the doctrine of marriage and sexual ethics, following the General Synod's support for the introduction of a service of blessing for same sex couples.