When Manser reached the age of eighteen, his mother Margaret gave him the Manor of Keisby, which had been granted to her for life by Geoffrey Luttrel for a yearly rent of 16 marks. In 1423, Manser made a 100l recognizance to the King to not harm William Gase, Parson of Dunsby church or any other person and in the same year promised to not harm any of the servants of Joan, Countess of Kent, and Humphrey, Earl of Stafford. In 1434 Manser took the oath not to maintain peace-breakers. In 1435 he attended the Shire Court at Leicester. By 1436, his income was £40 and he held one Knight's fee at Aslackby and Laughton. He was knighted between 1436 and 1441 and was appointed to Parliament as Knight of the Shire for Lincolnshire on 30 Jan 1447. He served in France in July 1448 and was Sheriff of Lincolnshire from 9 Nov 1448 to 26 Feb 1450. During the Lincolnshire feud between the wealthy and violent William Tailboys and the ex-Treasurer of England, Ralph de Cromwell, a Writ of Exigend was issued against Tailboys. Tailboy's powerful friend William de la Pole, 1st Duke of Suffolk and Lord High Admiral of England vigorously defended him from prosecution and is supposed to have pressured Sir Manser, then Sheriff, not to arrest Tailboys. Manser was punished for failing to carry out his duty but got off lightly due to Tailboys being pardoned. Manser's wife Elizabeth died in early 1449, and the income from her Leicestershire estate passed to her son and heir from her first marriage, Robert Walshale, Jnr. In 1450 Sir Manser went to France in the company of the Treasurer of the Household and newly appointed Lieutenant of Calais, Sir John Stourton. The cause of Manser's death is not known. He died before 25 Jun 1451, when a writ of Diem Clausit Extremum was issued to enquire upon his estate, whereupon his lands passed to his son and heir John.
Family
Between 1431 and 1435 Manser married Elizabeth, daughter and heir of John Wolfe, Esq. of Frolesworth and widow of Robert Walshale. Manser and Elizabeth had the following issue:-
John Marmion, fathered Mauncer. John and Mauncer Jnr both subsequently served as High Sheriff of Lincolnshire, in 1460 and 1497, respectively.
Manser's family "daughtered out" in the 1500s with his great-great-granddaughter Katherine Marmion. She married John Haselwood, Master of the Fleet Prison and had eleven children before remarrying to Thomas Claughton, Esq.
