Meredith had entered politics in 1872 as a Conservative, when he succeeded Sir John Carling (whose daughter, Jessie, married his brother Thomas) as London's representative to the Legislative Assembly of Ontario.

Charles Biggar, the biographer of Meredith's chief political rival, Sir Oliver Mowat, wrote, "There was no man in the ranks of the Opposition upon whom the choice could more worthily have fallen...

Especially in Committee of the Whole House, where details of legislation are worked out and party issues are for the moment forgotten, Mr. Meredith's services to the province were simply invaluable.

The Montreal Witness, a Liberal journal, declared him to be 'perhaps the most popular public man personally we have ever had in Canada'; and the House testified its appreciation of his services by voting him a salary of $2,000 per annum, which, however he declined to accept.

As a matter of conscience and increasingly frustrated by Macdonald's refusal to listen to him, Meredith launched an attack on what he saw as unfair advantages enjoyed by the separate Catholic schools.

In comparison to The Toronto Mail, his attacks were measured, but it was enough to draw the wrath of the Catholic population, which immediately swung their support firmly behind the Liberals.

In 1913, the Toronto World reported,[citation needed] "As a family the Merediths, whilst agreeable enough to those they meet have always held themselves aloof and have mixed little in society.

Outside of court Meredith still exercised great political influence, and his "legislative and forensic skills were frequently enlisted by various governments".

It was widely believed that Meredith was the political mentor of Sir James Whitney, and that he had a hand in framing some of the progressive measures put through by him.

Meredith also mediated between Whitney and Sir Adam Beck, suggesting and even wording many of the bills that established the Hydro-Electric Power Commission of Ontario.

He was also called upon to lead commissions into the causes for the collapse of the Farmer's Bank of York, Upper Canada and to investigate the worth of the Canadian Northern Railway prior to its takeover by the government of Sir Arthur Meighen.

As the Industrial Revolution created crowded factories and unsafe working conditions, injured workers and their families had few choices when it came to receiving benefits or compensation for their injuries.

In 1910, Sir James Whitney appointed Meredith to head the first Royal Commission to study workers' compensation systems throughout the world and to make recommendations.

In his royal commission report, Meredith said that the true aim of compensation law was to provide for the workman and his dependents and prevent their becoming a charge upon their relatives or friends, or the community at large.

That meant that workers would give up their right to sue their employers in exchange for guaranteed no-fault income security in the event of a workplace injury.

The Dictionary of Canadian Biography noted that, although severe, Meredith was considered dignified and courteous on the bench, and he was affectionately known as 'The Chief' among his fellow judges.

In 1913, The Toronto World reported:[citation needed] "Despite his seventy three years, Sir William is still a fine, erect and handsome man.

Donning a straw hat and gloves he delights to move about among his plants and bushes, weeding and clipping, or else to dig out dandelion roots from his lawn.