Sir James Altham (about 1554 - 1617), of Oxhey, Hertfordshire, was an English judge, briefly a member of the Parliament of England, and (from 1607) a Baron of the Exchequer. A friend of Lord Chancellor Francis Bacon, Altham opposed Edward Coke but advanced the laws of equity behind the fastness of the Exchequer courts, so long considered almost inferior. Through advanced Jacobean royalism he helped to prosecute the King's enemies and centralise royal power of taxation. With Sir Edward Bromley, he presided at the Lancashire witch trials in 1612.

James Altham was descended from Christopher Altham of Girlington, in the West Riding of Yorkshire. He was the third son (of five) of citizen and Clothworker James Altham (died 1583) of Mark Hall, Latton, in Essex, Sheriff of London in 1557–58, and sheriff of Essex in 1570, by his first wife. Alderman Altham was himself the son of Edward Altham (died 1548), a Master of the Fullers' Company, which had merged with the Shearmen in c. 1528–1530 to form the Worshipful Company of Clothworkers: Edward, although never an alderman, served a term as Sheriff of London in 1531-32 together with Richard Gresham, in the mayoralty of Sir Nicholas Lambert. Edward, who requested burial at St Martin Outwich, in Bishopsgate, left his properties in Dagenham and Barking to his son James and to the heirs of his body.

James Altham's mother was the alderman's first wife Elizabeth Blancke (married January 1548/49), daughter of Thomas Blancke of London, Haberdasher (died 1562), and sister of Sir Thomas Blanke, Lord Mayor of London in 1583. The elder Blanke had built for himself the mansion of "Abbottes Inne", on the historic site of the Abbot of Waltham's house in the London parish of St Mary-at-Hill. Elizabeth Altham died in childbirth in 1558 and received a public funeral at St Martin's church. After this alderman Altham became the fourth husband of Mary Matthew, successively the wife of one Woolley, of the citizen and Skinner Thomas Langton (died c. 1550), and of Sir Andrew Judde (died 1558).

As a consequence of this marriage, James Altham junior became the step-brother of Mary Langton, wife of Admiral Sir William Wynter. His stepmother, Dame Mary Judd, was, together with James and his brothers Thomas and Edward, the alderman's executor in March 1582/83: she lived down to 1602. The eldest brother becoming Roman Catholic, Mark Hall at Latton was inherited by the second brother Edward (died 1605), and descended to his heirs. On 16 June 1584, James Altham married his first wife Margaret Skynner at St Dunstan-in-the-East. With the death of Sir Thomas Blancke in 1588, the Blancke properties in London devolved in remainder upon Thomas Altham (then of Oxford, aged 38) or Edward Altham, subject to a lifetime occupancy for the widow Dame Margaret Blancke.

James Altham followed his elder brothers to the University of Cambridge (where they had matriculated as fellow-commoners from Clare College in 1567, before being admitted together to Lincoln's Inn in 1570). "Specially admitted" a fellow-commoner at Trinity College, Cambridge in 1571, he entered Gray's Inn in 1575 and was called to the bar in 1581. Following his marriage, he is mentioned in Croke's reports for the first time as arguing a case in the Queen's Bench in 1587. Shortly before he entered the Commons, he was made an Ancient of Gray's Inn, granting superior status over juniors at the all-important dinners. In 1589, he was elected M.P. for Bramber in Sussex. For some unknown reason there are no surviving records of Altham's activities during the sessions. All that has come down is his drafting of seven bills for the Parliament of 1601, during which Robert Cecil, 1st Earl of Salisbury passed some of the most significant social laws of the period.

In 1595, when the resignation of Thomas Fleming as Recorder of London (1594–1595) was contemplated in preparation for his appointment as Solicitor General, the Queen invited the city to propose names to be considered for his successor. The citizens, fearing that it might be intended to curtail certain of their traditional liberties, decided to propose one name only, that of James Altham, as one who might be expected to uphold their interests. Sir John Spencer, Lord Mayor (1594–1595) wrote of him in a letter to the Lord Treasurer:

"And, for mine own opinion, my good Lord, as also of many others, we have one born and dwelling among us, whom we have great experience of, and think very able to do us service in this behalfe. His name is Mr. James Altham, son of Mr. Altham, late of Essex, Esq., he is a Bencher of Gray's Inn, and one of our ordinary Sworn Counsellors of the City, well acquainted with our customes, and very well thought of for his honestie and skill in law, both throughout the whole City, and elsewhere, and being in election last time, did very narrowly miss it: in which respects, and for the good hope we have of him, myself and many others do, only for the good of the City, earnestly wish him the place, if her Majesty shall please to remove the other; nothing doubting, but that her most excellent Majesty, and your good Lordship, and my other Lords, will take very good liking of him..."

Altham, however, was passed over a second time, in favour of John Croke.