He represented Cambridge in the Short and Long Parliaments of 1640, and at once showed extraordinary zeal and audacity in his opposition to the government, taking a large share in business and serving on numerous and important committees. As the cousin of Hampden and St. John he was intimately associated with the leaders of the parliamentary party. His sphere of action, however, was not in parliament. He was not an orator, and though he could express himself forcibly on occasion, his speech was incoherent and devoid of any of the arts of rhetoric. Clarendon notes on his first appearance in parliament that "he seemed to have a person in no degree gracious, no ornament of discourse, none of those talents which use to reconcile the affections of the standers by; yet as he grew into place and authority his parts seemed to be renewed." He supported stoutly the extreme party of opposition to the king, but did not take the lead except on a few less important occasions, and was apparently silent in the debates on the Petition of Right, the Grand Remonstrance and the Militia. His first recorded intervention in debate in the Long Parliament was on the 9th of November 1640, a few days after the meeting of the House, when he delivered a petition from the imprisoned John Lilburne. He was described by Sir Philip Warwick on this occasion:--"I came into the House one morning well clad and perceived a gentleman speaking whom I knew not, very ordinarily apparelled; for it was a plain cloth suit which seemed to have been made by an ill country tailor; his linen was plain and not very clean; ... his stature was of a good size; his sword stuck close to his side; his countenance swollen and reddish; his voice sharp and untunable and his eloquence full of fervour ... I sincerely profess it much lessened my reverence as to that great council for he was very much hearkened unto." On the 30th of December he moved to the second reading of Strode's bill for annual parliaments. His chief interest from the first, however, lay in the religious question. He belonged to the Root and Branch party, and spoke in favour of the petition of the London citizens for the abolition of episcopacy on the 9th of February 1641, and pressed upon the House the Root and Branch Bill in May. On the 6th of November he carried a motion entrusting the train-bands south of the Trent to the command of the earl of Essex. On the 14th of January 1642, after the king's attempt to seize the five members, he moved for a committee to put the kingdom in a posture of defence. He contributed £600 to the proposed Irish campaign and £500 for raising forces in England--large sums from his small estate--and on his own initiative in July 1642 sent arms of the value of £100 down to Cambridge, seized the magazine there in August, and prevented the king's commission of array from being executed in the county, taking these important steps on his own authority and receiving subsequently indemnity by vote of the House of Commons. Shortly afterwards he joined Essex with sixty horse, and was present at Edgehill, where his troop was one of the few not routed by Rupert's charge, Cromwell himself being mentioned among those officers who "never stirred from their troops but fought till the last minute."