In 1853 when, at the age of 21, he entered the Elphinstone Institution (later Elphinstone College). Here, he encountered Western liberal thought and the ideals of the Indian Renaissance, which kindled his passion for social reform. Mulji quickly became involved with progressive groups such as the Buddhi Vardhak Hindu Sabha, established in 1851, which promoted knowledge and rational thinking.

Mulji's pen found its first home in 'Rast Goftar' (Truth Teller), founded by Dadabhai Naoroji in 1851. Here, in articles such as 'Baap Daadao Ni Chal' (The ways of our forefathers), he advocated selective modernisation that preserved Indian identity. Mulji articulated a nuanced stance on social reform that would characterize much of his later work. He argued against the notion that reform necessarily meant wholesale adoption of British culture. His early essays in 'Rast Goftar' also tackled pressing social issues such as child marriage and the education of girls.

Yet reform exacted personal costs. In 1853, Mulji's participation in an essay contest on widow remarriage so enraged his aunt that she evicted him from her home. He won the Kellar scholarship and became a schoolteacher to support his family and studies.

In 1855, Mulji founded 'The Satya Prakash', a Gujarati newspaper to spread his message of social reform. His fearless critiques questioned entrenched social and religious practices.

It was around this time that a massive row erupted between the Vallabhacharya sect, whose religious leaders were known as Maharaj, and the Shaivite Brahmins.

The conflict was centred on ritual purity and the acceptability of food offerings. The Vallabhacharya Maharaj raised the issue that prasad (food offerings) given to Lord Shiva, the principal deity of Shaivism, could not be consumed by Vaishnavites.

“However, the Vallabhacharya Maharajas seized upon this event to assert sectarian boundaries. They decreed that unless the Shaivite Brahmins apologised for allowing Vaishnavites to partake in offerings meant for Shiva, Vaishnavites should withhold all donations to Shaivite causes. To press their demands, the Maharajas went so far as to close the doors of their temples to Vaishnavites,” according to a book titled Karsandas Mulji – Jeevan Nondh, by Makrand Mehta and Achyut Yagnik.

The Maharajs' demands later extended beyond the immediate issue of food offerings. They insisted that no Vaishnavite follower should take a Maharaj to court, that Vaishnavites be prohibited from writing anything against the Maharajas, and that if a non-Vaishnavite attempted legal action against a Maharaj, the Vaishnavite community should unite to fund a legal defence that would preclude the Maharaj from having to appear in court personally, it said.

These events provided fertile ground for Karsandas Mulji's critiques. In his column, Mulji began writing scathing articles about what he saw as the Maharajs' attempts to consolidate power and evade accountability.

Mulji's commentary so rattled the religious leaders that they allegedly attempted to silence him with a substantial bribe — a dakshina (donation) of ₹10,000, an enormous sum at the time, according to the book. Mulji rejected the offer.

The watershed moment in Mulji's career came on September 21, 1860, when he published an article in his newspaper which roughly translates into, ‘The real religion of Hindus and the current hypocritical sects’. It was a searing indictment of practices within the Vallabhacharya sect of Hinduism, particularly focusing on the conduct of its spiritual leaders, the Maharaj.

Mulji alleged that these revered figures had twisted the concept of ‘Rās Līlā’ to justify sexual relations with female devotees, many of whom were married.

Mulji did not mince words, describing the behaviour of the Maharaj as "adulterous" and accusing them of "defiling the wives and daughters of their devotees." He criticised their lavish lifestyles and practices such as "Choranyu Prasad," where devotees consumed the Maharajas' leftovers, including bathwater, as blessed substances. Mulji’s article called these practices a "fraud" and urged readers to return to what he considered the pure, primitive religion of the Hindus.

A religious leader Jadunathji Maharaj took offence and filed a ₹50,000 defamation suit against Mulji, setting the stage for the historic Maharaj Libel Case of 1862.

For Karsandas Mulji, the case represented more than just a personal defence; it was an opportunity to put the very institutions of religious authority on trial. His legal team, which included the renowned Parsi lawyer Kharshedji Nasarvanji Cama, mounted a vigorous defence that sought not only to prove the truth of Mulji's claims but also to challenge the broader system that enabled such abuses.

Throughout the trial, witness after witness came forward with testimony that corroborated Mulji's allegations. The proceedings laid bare the stark contrast between the ascetic ideals preached by the sect and the reality of how some of its leaders lived.

In a groundbreaking verdict delivered on April 22, 1862, Sir Joseph Arnould, the presiding judge, ruled in favour of Karsandas Mulji. It was a resounding vindication of Mulji's crusade for reform and a damning indictment of the abuses within the Vallabhacharya sect.

"A public journalist is a public teacher. The true function of the press, that by the virtue of which it has rightly grown to be one of the great powers of the modern world - is the function of teaching, elevating and enlightening those who fall within the range of its influence," the court said, lauding Mulji's journalism.

The court ordered Jadunathji Maharaj to pay ₹13,000 in damages to Mulji, who had spent ₹11,500 on his defence.

In the annals of Indian legal history, few cases have had as profound an impact on religious reform and freedom of expression as the Maharaj Libel Case of 1862. The case was called the “greatest trial of modern times since the trial of Warren Hastings”. The case turned Mulji from a local troublemaker into a symbol of resistance against religious leaders' abuse.

Beyond journalism, Karsandas Mulji was a prolific writer whose works sought to educate and enlighten. His book "Nibandhmala" (Garland of Essays), published in 1860, was one of the first collections of essays in the Gujarati language. He also translated John Stuart Mill's "Utilitarianism" into Gujarati, making influential Western philosophical ideas accessible to Indian readers.

Today, Mulji's story resonates anew with the recent controversy surrounding 'Maharaj,' a Netflix film based on the 1862 libel case. Starring Aamir Khan's son Junaid, the film's June 14 release has been stayed by the Gujarat high court for now. While the 'Maharaj' waits for the high court’s green light, Karsandas Mulji's legacy endures.