The Dorriens were of Hamburg merchant stock and settled in London in the early 18th century. Magens’s father, John Dorrien, was a partner in the house of Dorrien and Mello of Billiter Square and in that of Boctefour, Dorrien & Co. of Old Jewry; from 1772 he was also a partner in the bank of Dorrien, Rucker and Carlton of 22 Finch Lane, Cornhill. On his death in 1784 Magens, who was left over £13,000 and an estate at Brightlingsea that had belonged to his uncle Nicholas Magens the army contractor (d.1764), became a partner in the bank, subsequently known as Dorriens, Mello, Martin and Harrison. He remained associated with it until its amalgamation with Curries’ in 1842.
Magens owed his political debut to his wife’s family, the Dinevors, who encouraged him to offer both for the borough and county of Carmarthen in 1796. The latter was a forlorn hope, but he was at first successful in the borough election, only to be unseated on petition. Had he held the seat, it would have been as locum tenens for the first available member of the Dinevor family.
Magens was listed a supporter of Pitt’s second ministry in September 1804 and July 1805. His interest in the silver coinage prompted his first contributions to debate, 27, 29 Mar. 1805, and he opposed the Irish silver tokens bill, because he regarded tokens as little better than paper money and no substitute for the restoration of a silver coinage, 3 May. He was also interested in the linen trade, 7 May 1805, and on 9 June 1806 opposed the linen drawback bill. He supported the Grenville ministry’s repeal of Pitt’s Additional Force Act, 30 Apr. 1806, and was listed friendly to their abolition of the slave trade, but voted against them on the Hampshire election petition, 13 Feb. 1807. On 22 Apr. 1807 he was teller against the prosecution of a resident of Penryn for election irregularities. He was well disposed to the Portland administration, to whom Lord Dinevor applied on his behalf for a baronetcy. On 10 Aug. 1807 he was a spokesman for the West India sugar planters.
Magens rallied to Perceval’s ministry on the address, 23 Jan., and on the Scheldt question, 26 Jan., 23 Feb., 5, 30 Mar. 1810. The Whigs listed him ‘Government’ at that time. He voted against sinecure reform and against parliamentary reform, 17, 21 May 1810. He sided with ministers on the Regency, 1 Jan. 1811. But he spoke only on the currency problem: he had promised the House to do so, 1 Feb. 1810, and, on the report of the bullion committee, 13 May 1811, announced, as a select committeeman, that he agreed with the chairman as to the depreciation of paper currency and wished to see cash payments resumed as early as possible. On 10 Apr. 1812 he opposed the bank-note bill, as being likely ‘to throw the country into a state of instability’. He was a die-hard opponent of Catholic relief, 22 June 1812.
Magens was elected to but did not take his seat in the Parliament of 1812, his patron having sold his interest in the seat. He was never again in the House. He died 30 May 1849, aged 87.