The Solemn Engagement (A Solemne Engagement of the Army, under the Command of his Excellency Sir Thomas Fairfax) was a declaration to the English House of Commons adopted unanimously by the General Council of the Army commanded by Thomas Fairfax at Newmarket on 29 May 1647.
This was in part because of weeks of arrears owed to the soldiers, and in frustration of the slow progress parliament had made in securing a settlement with the imprisoned Charles I.
[1] The agreement was read, and assented to by all the officers and soldiers of the regiments of the New Model Army that rendezvoused on Kentford Heath near Newmarket on Friday and Saturday 4 and 5 June.
[2] In the letter he explained that because the King was now with the Army (Cornet Joyce having taken Charles I from Parliament's custody at Holdenby House), it had been agreed on 7 June that Charles would be held at Newmarket under the guard of two regiments of Ironsides.
The Army rejected the commissioners offer and continued their slow advance towards London.