At the start of the
First English Civil War in August 1642, Birch was a captain in the
Bristol militia and served with the
Parliamentarian garrison. He later recorded that some of his men viewed the war as a break from routine, with better pay and rations than in civilian life and were concerned it might end too soon. After the
Royalists captured
the town in June 1643, the garrison was given a pass to
London. With the help of Sir
Arthur Haselrig, Birch was commissioned in the army commanded by
William Waller, and quickly proved an energetic and courageous officer. In November 1643, he served in the first
Siege of Basing House, and was slightly wounded in the
Battle of Alton on 13 December. Less than a week later, he was shot in the stomach in an
assault on Arundel Castle, allegedly surviving only because the cold weather stemmed the flow of blood. Birch recovered in time to fight at
Cheriton in March 1644, a Parliamentarian success that forced
Charles I onto the defensive in
South East England. At
Cropredy Bridge in June, he commanded the rearguard that held the bridge long enough to allow Waller's main force to retreat. Shortly after this, Birch raised a regiment of infantry which was shipped to
Plymouth to reinforce the garrison. He spent the rest of the war in
South West England and the
Welsh Marches. Although not part of the
New Model Army, his unit took part in its 1645 Western Campaign including the capture of
Bridgwater and
Bristol. On 17 December 1645, Birch led a surprise night-time attack on the Royalist garrison of
Hereford, which had recently repulsed a
month-long siege by Scots
Covenanters, and the Royalist commander
Barnabas Scudamore was later accused of betrayal. Appointed Governor of Hereford, Birch also fought at
Stow-on-the-Wold in March 1646, the last major battle of the war, and captured
Goodrich Castle in June, just before the war ended. However, victory resulted in increasingly bitter disputes over the post-war political settlement between radicals within the New Model like
Oliver Cromwell, and the moderate party in Parliament, which included his former commander William Waller, and
Denzil Holles. At the same time, Parliament's desperate economic position made reductions in the military a matter of urgency. Birch became involved in a struggle with the other regional Parliamentarian commander,
Edward Harley, as both men sought to ensure their troops were the ones retained. One of the few members of the local
landed gentry to support Parliament in 1642, Harley defeated Birch in 1646 as
MP for
Herefordshire. Despite this setback, in September Birch was elected for
Leominster, but under the
Self-denying Ordinance was required to give up his military commission. Appointed
High steward of Leominster in 1648, he also invested heavily in purchasing church lands, which made him extremely wealthy. Disputes over a peace settlement with Charles I and religious policy split
Parliament between moderates like Birch, and more radical
religious Independents such as
Oliver Cromwell, including his cousin
Thomas Birch. After the
Second English Civil War he was excluded from Parliament in
Pride's Purge of 6 December 1648. ==1660 Restoration and after==