He emigrated to the Massachusetts Bay Colony, becoming a founding father there, setting up a stock company, acquiring estates, and establishing a milling business.
[1] He trained as an attorney, and was involved with his brothers in maritime import and export from the nearby port of Southampton, becoming a competent seaman and attaining the status of "master".
[2] Dummer became closely associated with the radical Puritan malcontent Stephen Bachiler, who wanted to take his flock at Newton Stacey (near Wherwell, Hampshire) to New England.
They had settled on the territory bordering on the Parker River as a suitable place for the keeping of the cattle because of the fertility of the upland and the large quantity of salt marsh, considered of special value for the forage.
[2] In England a great body of people from the Hampshire Avon and Test valleys of all trades assembled at Southampton and London to sail in an initial convoy of 10 ships.
[2] In March 1635, Dummer and John Spencer, came round in their shallop, came ashore at the landing at a spot known by the "Indians" as Winnicunnet and were much impressed by the location.
Spencer was a partner in the cattle importation venture, and they "spotted what an asset to a prosperous settlement would be the several thousand acres of fine salt hay, just waiting to be cut or even fed off in pasture".
[8] Liberty was also granted to Dummer and to John Spencer to build a mill and weir at the falls at Newbury, to enjoy to them and their heirs forever.
Dummer's wife, Mary, was a follower of Williams and Anne Hutchinson during the Antinomian Controversy, leading to her and Richard becoming banished to Boston.
John Eliot said this of her later: She was a Godly woman but by the seduction of her acquaintances she was led away into the new opinions in Mrs Hutchinson's time, and her husband removing to Newbury, she there declared herself and did also with others endeavours, seduce her husband and persuaded him to return to Boston, where she being young with child and ill; Mr. Clarke (one of the same opinions) unskillfully gave her a vomit, which did in such manner torture and torment her with the rising of the mouth, and other violences of nature, that she died in a most uncomfortable manner.
[9] Following Mary's death, Dummer, having been disenfranchised with many others as result of his support for Williams and Henry Vane, left the province and returned to Southampton.
[2] On his return to the family home at Bishopstoke, Dummer found his brothers packing and storing goods and provisions for their forthcoming journey to New England.
The royalist High Sheriff, Sir John Oglander, kept his eye on happenings and noticing Richard's ship, the Bevis of Hampton, at anchor at Southampton, put a detention order on it while he investigated what was going on.
Although they failed to turn up any contraband or evidence of tax evasion on exports, the searches did reveal the provision the family were making for their forthcoming voyage.
[2] Dummer had six children: In 1631, prior to his first going to New England, he settled a rent-charge of 40 shillings per annum, out of his lands in Bishopstoke, for the use of the poor of the parish at Michaelmas and Lady Day forever.
In the subscription that followed, Dummer made the largest contribution with a donation of £100, one fifth of the total, in spite of having suffered under Winthrop in earlier years.