He was apparently a Londoner who spent some time in Amsterdam, where he was acquainted with John Robinson and probably John Smyth. He adopted in the main the principles of the Brownists, and after his return to England Busher apparently became a member of the congregation of Thomas Helwys.
Busher's only published work was entitled Religious Peace; or, a Plea for Liberty of Conscience, long since presented to King James and the High Court of Parliament then sitting, by L. B., Citizen of London, and printed in the year 1614; no copy of this 1614 edition is known. His treatise advocating religious toleration. In it he speaks of his poverty, due to persecution, which prevented his publishing two other works he had written: (1) ‘A Scourge of small Cords wherewith Antichrist and his Ministers might be driven out of the Temple;’ and (2) ‘A Declaration of certain False Translations in the New Testament.’ Neither of these books appears to have been published, nor is any manuscript known to be extant. Religious Peace was reissued in 1646 (London), with an epistle ‘to the Presbyterian reader’ by H. B., probably Henry Burton. This edition was licensed for the press by John Bachilor, who was on its account ferociously attacked by Thomas Edwards (Gangræna, iii. 102–5).
A reprint of the 1646 edition, with an historical introduction by Edward Bean Underhill, was issued by the Hanserd Knollys Society in 1846. According to David Masson, Busher's book ‘is certainly the earliest known publication in which full liberty of conscience is openly advocated’ (Masson, Milton, iii.102). It has been suggested that James I was influenced by it when he declared to parliament in 1614, ‘No state can evidence that any religion or heresy was ever extirpated by the sword or by violence, nor have I ever judged it a way of planting the truth.’