Irby’s father did not follow other members of his family by pursuing a legal career, but dabbled in trade, becoming a member of the Levant Company; he died in 1610, when Irby was only five years old.
Irby contested the 1628 election for Boston, his opponent being Richard Oakeley*, the nominee of the bishop of Lincoln. Although narrowly outvoted on the corporation, he obtained 67 votes from the freemen, whose right to participate was uncertain. On petition he established the wider franchise, but it took more than seven weeks for the Commons to rule that he had won the seat.
During his shrievalty in 1637 Irby emerged as one of the leaders of resistance to Ship Money in the county. He aroused opposition by altering the assessments to help poorer areas, ending up some £2,662 in arrears. The Council believed that his tardiness in paying over the money was deliberate, and he was threatened with a Star Chamber prosecution.
