Nothing is known of his early career except that in April 1544 he was involved with the Earl of Lennox in armed opposition to the Regent Arran at the battle of Glasgow, for which he later received remission.
After the siege of Leith, Richardson sat as a prelate at the Reformation Parliament of 1560 and was listed by Knox among those "that had renunceit Papistrie and oppinlie profest Jesus Chryst with us.".
Three charters by the commendator and convent of Dunfermline on 28 July 1563 conveyed to him extensive lands, mainly in Haddingtonshire, Edinburghshire, and Fife, amounting to no fewer than seventy-seven farms and scattered holdings.
Crawfurd wrote of Richardson: He appears to have been a very wise moderate man; for so far as I can observe from the history of these times, he kept himself more in a neutrality, and was less a party-man than any other that held any great office about the court.
His support for the new regime is also evidenced by a loan of £5,000 Scots to the Earl of Moray, now the Regent of Scotland, on 17 September 1567, secured on a pledge of a selection of the queen's jewels.
[5] He raised money for Regent Moray by pawning more of the personal jewellery of Mary, Queen of Scots, including a gold chain belt of pearl knots and a hair garnishing with 57 diamonds which his son James Richardson returned to Holyrood Palace on 18 March 1580.
[6] In 1570, as he was "greitlie superexpendit as treasurer and unable to pay his creditors" Regent Moray gave him the revenue arising from wards and marriages and vacant benefices.
Thereafter he continued to receive money from the mint to redeem the royal jewels that had been pledged to him, further payments being made to his sons after his death, which probably took place between May and November 1578.