Prince Charles described John Henry Newman as a “fearless defender of the truth” after the British cardinal became a saint in front of an estimated 20,000 pilgrims in St Peter’s Square.

Newman, also a theologian, scholar and poet, was regarded as one of the most influential figures of the Victorian age and is the first Briton to be made a saint since 1976, when John Ogilvie was canonised by Pope Paul VI.

“In this age, during which he has been made a saint, Newman’s example remains compelling and relevant,” Charles said during a reception after the canonisation in Vatican City on Sunday.

“He was able to advocate without accusation and, perhaps most of all, to see differences as places of encounter rather than exclusion … these are principles that continue to inspire and to guide each new generation.

“Today is a cause of celebration for us all … he was a priest, poet and thinker ahead of his time, and perhaps above all, he was a fearless defender of the truth whose impact on the world was as profound as it is enduring.”

Newman, born in London in 1801, was a Church of England priest before controversially converting to Catholicism in 1845.

His journey towards sainthood began after the Vatican declared that it was due to his intercession that two people, Jack Sullivan and Melissa Villalobos, were miraculously cured from serious illnesses. Sullivan, an American deacon who had suffered a spine condition, and Villalobos, who suffered life-threatening complications when pregnant with her fifth child, attended the canonisation.

Sullivan, who had been told he would end up paralysed, described the pain endured as “being on a higher level than a woman going through labour”. Newman was beatified in 2010 after Pope Benedict XV approved Sullivan’s recovery.

Pope Francis then credited Newman with curing Villalobos, who went on to have two more children.

“It’s such a joyous day for me to see Newman become a saint,” Villalobos said. “I feel like I’ve been waiting for this since the minute I was created and here it is. Some people lived an entire life hoping for his canonisation and it never came, so it’s a real blessing to see it and be part of it.”

Both Sullivan and Villalobos, from Chicago, became devoted to Newman after watching a show dedicated to him on EWTN, a Catholic TV channel.

“I was struck by his tenderness, which came across when I read his letters,” added Villalobos. “He was a colossal genius, an intellectual powerhouse. And he also had a tremendous loving heart.”

Newman was declared a saint by Pope Francis alongside four women – Brazilian sister Maria Rita de Sousa Brito Lopes Pontes; Swiss laywoman Marguerite Bays; Indian sister Mariam Thresia and Italian sister Giuseppine Vannini.

He was known as a powerful preacher whose sermons could change lives. Some 15,000 people lined the streets for his funeral in Birmingham in 1890.

Linda, a lay chaplain from Nottingham who did not wish to give her surname, travelled to Rome with her family. She said: “For me, Newman was a person who struggled but never gave up. He wanted the laity to have knowledge, not just blindly follow the faith.”

It was after a trip to Rome in 1833 that Newman felt called to the Oxford Movement, which sought to renew the Church of England by returning it to its Catholic sources. On converting to Catholicism, he instructed bishops to “listen to the laity”.

Newman also helped reform Oxford University and founded University College Dublin.

“Newman represents integrity and the importance of struggling to find wholeness in the self,” said Vincent Nichols, Archbishop of Westminster. “His view on education, for example, was very much against the manipulation of education purely for economic reasons.”

• This article was amended on 29 October 2019. A previous version referred to Maria Rita de Sousa Brito Lopes Pontes as “Dulce Lopes Pointes”. This has been corrected.