The veteran entertainer and artist Rolf Harris is facing prison after being found guilty of indecent assault following a trial in which he was portrayed as a "Jekyll and Hyde" character who used his celebrity status to grope and abuse young women and girls.

Following a dramatic six-week hearing, the jury at Southwark crown court convicted Harris of 12 counts of indecent assault, from 12 initial charges dating over nearly two decades from 1968.

The judge, Mr Justice Sweeney, said the entertainer would be sentenced on Friday, pending medical reports, and warned Harris a jail term was "uppermost in the court's mind". Harris will remain on unconditional bail until Friday.

Speaking outside the court, DCI Mick Orchard of the Metropolitan Police Service said: "[Harris] committed many offences in plain sight of people as he thought his celebrity status placed him above the law."

"I want to thank the women who came forward for their bravery, I hope today's guilty verdict will give them closure and help them to begin to move on with their lives."

"Today's case and verdict once again shows that we will always listen to, and investigate allegations regardless of the time frame or those involved."

Jenny Hopkins, of the Crown Prosecution Service, praised Harris's victims for coming forward. "The victims in the this case have suffered in silence for many years … I hope today's verdict provides other victims with the courage and confidence to come forward no matter who is alleged to have carried out the abuse and when," she said.

The prosecution presented the 84-year-old Australian-born star as an arrogant and reckless serial molester who treated his victims as "sexual objects to be groped and mauled when he felt like it".

"He targeted fans who were mesmerised by his fame and talents," the prosecution QC, Sasha Wass, told the jury. "He was a children's entertainer and they were beguiled by his singing and painting. And the penalty of their admiration was to suffer sexual assault."

The Harris family, who like the entertainer sat grim faced and silent as the verdicts were read out, filed out without saying a word. As Harris was ushered to a small chamber the family gathered in another room, hugging each other but saying nothing to the watching media.

The entertainer's team of ever-present security guards could be heard discussing how to bring in extra staff to usher Harris past the huge mass of media outside the court. Harris's PR firm, Bell Pottinger, taken on for the trial, released a statement saying he and the family would say nothing today.

DCI Michael Orchard, who led the police investigation, was due to address the press with a CPS representative outside court later.

The court had heard evidence from 10 different women about alleged assaults by Harris, none of whom knew each other aside from a mother and daughter who claimed they were groped together. Many of the women described similar experiences, Wass said, and it was absurd to suggest this was just coincidence given the disparate and unconnected group of alleged victims.

Harris's lawyers, however, insisted that the standard of proof was not nearly high enough. "Making allegations loudly and forcefully does not make them true," defence counsel Simon Ray told the court.

Even before the verdict the court case shattered Harris's public persona as a cuddly family entertainer, one maintained over six decades of stardom. Harris admitted having sexual relations with the best friend of his daughter Bindi Nicholls – a girl 35 years his junior whom he had known since she was two, beginning when she was staying at his family home. Harris insisted this began when the friend was 18, not 13 as she claimed.

Rolf Harris at court with daughter Bindi, wife Alwen and Niece Jenny, earlier this month. Photograph: Alex Huckle/GC Images

Pressed by Wass during a long and crucial cross-examination, Harris conceded that the long affair, which lasted until the woman was in her late 20s, showed he had a dark side that he was adept at concealing from others.

He also suffered a key reverse when his insistence he could not have groped one alleged victim in Cambridge in the 1970s as he had not visited the city until many years later was demolished after a member of the public sent in video footage of Harris taking part in a TV show filmed there in 1978.

The allegations connected to the close friend of Nicholls, which formed seven of the 12 counts, were always set to be crucial to the jury's deliberations. Unlike with other allegations the entertainer could not dismiss all connection to the alleged victim, someone he had known since the age of two. Arguably most damaging was a letter sent to the woman's father in the mid-1990s, in which he confessed having a long sexual relationship with her, albeit one he said began when she was 18, not, as she said, 13.

During his long stint in the witness stand, Harris was questioned at length about why he expressed abject remorse to the father for his actions, offering a little more credible explanation than he felt ending the relationship had upset the woman.

What bolstered her case was evidence showing she had given a virtually identical story to a series of counsellors and therapists for more than 15 years, based on their professional notes she allowed the court to see. It was perhaps a factor in the jury's deliberations that Nicholls also underwent counselling on learning of her father's affair, but opted not allow her own notes to be released.

While the evidence presented in court covered a full 10 alleged victims, what the jury was not told was that seven more complainants alleged Harris groped or assaulted them, claims covering almost 30 years and involving women and girls aged from 14 upwards. These accounts were given in pre-trial hearings, but were not pursued in the main trial for legal reasons.

One woman said she was 14 in 1977 when Harris, on a visit to Sydney, grabbed her bottom and pursued her into another room, saying, "Rolfie deserves a cuddle". Other alleged assaults took place at a fete in Harris's home village of Bray, Berkshire – a woman said she was aged 13 or 14 when Harris said he liked her jumper and "wanted to see what was underneath it" – and at a party in a pub for the broadcaster Michael Parkinson, where a woman working at the bar said Harris kissed her neck.

Another witness, a well-known British celebrity who, like the other complainants, cannot be named for legal reasons, said Harris played with her underwear as she recorded a TV interview with him in the mid-1990s. Making an unsuccessful application for the woman's evidence to be included in the trial, Wass said the incident took place in "a very public place". She said: "The indecent assault took place with the defendant's hands going under her clothing and up her thigh, and higher still when she abruptly drew the interview to a halt. She said that the defendant's hands cupped her buttocks and she described what she felt as groping."

Additionally, new complainants came forward in Australia during the trial, among them a radio host and a TV newsreader.

Jane Marwick, a radio presenter in Western Australia, said Harris groped her breast while posing for a photo with her and her co-host after a 2001 interview. "Rolf Harris had been one of my childhood idols growing up here in WA," she told Australian media during the trial. "I'd thought the world of him and I couldn't believe this was happening."

Her co-presenter, Gary Shannon, said he recalled seeing Harris carry out the grope: "He had his tongue out and was panting heavily. He grabbed the wobble board and bolted out of the studio." Separately, Verity James, a newsreader for ABC, told reporters she and a female producer were groped by Harris during a radio interview in 2000.

One of the curiosities of the case was that for his six-decade showbusiness career, Harris did not have the raft of celebrity character witnesses provided by other entertainers facing similar trials recently. Despite whispered hints by his PR team about big names to come, the most star power summoned up by the defence was the former Crimewatch presenter Sue Cook and Paul Elliott, a theatrical impresario known as the "king of pantomine".

The NSPCC tweeted: "Once more we've seen that victims of sexual abuse are not alone and that they will be listened to when they contact our helpline". The charity said it had received 28 calls about the entertainer to its helpline - including 13 people who said they had been abused by him.

Harris's career began when he arrived in London from Perth in 1952 and was diverted from a planned destiny in art through performing in cabaret and then children's TV. Over the decades he hosted prime-time entertainment shows, had a series of novelty pop hits and presented cartoon programmes and then animal shows.

Much of his career was based on his skilled and rapid sketching and he eventually acquired some renown as a serious artist, painting a portrait of the Queen in 2006.