He was Sheriff of London from 1621 to 1622 and Master of the Haberdashers Company for the first time in the same year: he transferred as alderman to the Langbourn ward in 1626.
In 1624 the theologian Thomas Gataker (1574-1654) published a volume Iacobs Thankfulnesse to God, for Gods Goodness to Iacob, dedicated jointly to Sir William and to Mr George Whitmore, opening his address by stating that their mother had presented him and spoken for him at baptism, as his godmother.
His texts, which concern the promise that God will advance the temporal affairs of those who attend to the spiritual, are, he says, "to egge you on, whom God hath blessed with so large a portion of his bounty, unto those religious offices, that by occasion of Iacobs example, men of your rancke are therein encited unto, whether risen from meane estate, as with him here it had beene, or from the first largely and liberally endowed, as your selves".
Thomas Heywood published an account of all the pageants and triumphs which attended his inauguration, and in his dedicatory letter wrote: "...of you it may be undeniably spoken: that none ever in your place was more sufficient or able, any cause whatsoever shall be brought before you, more truly to discerne; being apprehended more aduisedly to dispose, being digested, more maturely to despatch.
[1] In 1641, he received King Charles I at Balmes Manor,[1] which had been purchased for him in 1634 by his elder brother Sir William Whitmore of Apley,[11] High Sheriff of Shropshire in 1620.