Stepbrother of Parliamentary leader John Pym, he joined him in opposing Arminianism in the Church of England, and played a leading role in the impeachment of Archbishop Laud.

There are few details of his life prior to 1626, although he produced several books,[5] and Rous claimed in 1641 that he spent some of 1609 travelling in Europe with Sir Thomas Overbury, victim in one of the most famous murder cases of the period.

Rous and Pym led the attack on Roger Maynwaring and Robert Sibthorpe, two clergymen who published sermons supporting divine right of kings, and passive obedience.

In a speech made in January 1629, Rous argued if Arminianism continued to spread, 'true religion' was doomed; this inspired much of the subsequent opposition to Archbishop Laud.

[8] Returned for Truro in the elections of April and November 1640 Long Parliament, Rous opened the debate on the legality of Laud's reforms in December 1640, and presented articles of impeachment against John Cosin in 1641.

[9][10] After 1647, Rous moved closer to the Independents like Oliver Cromwell, and supported Charles' execution in 1649; since Presbyterians believed a 'well-ordered' monarchy was divinely mandated, The Protectorate presented a problem.

[11] In April 1649, he published a pamphlet titled The Lawfulness of Obeying the Present Government; claiming to be written by a 'true Presbyterian', this argued scripture required obedience to authority, regardless of who wielded it.

In a pre-planned move, on the morning of 12 December 1653, he led moderate members to Cromwell's office, where they resigned 'their powers unto his Excellency', effectively dissolving Parliament.