Enlisted in the Eastern Association army, Packer was a trusted lieutenant in Oliver Cromwell's cavalry regiment by 1644. A religious radical, Packer clashed with Major-General Lawrence Crawford, who had him arrested for disobedience.
Packer joined the Eastern Association army and became a trusted subordinant to Oliver Cromwell's cavalry force by 1644. As a fervent nonconformist, Packer clashed with Major-General Lawrence Crawford, who subsequently arrested him for refusing orders.