It wasn't until the age of 16 that Joseph considered an acting career and trained at the Rose Bruford College in London. Joseph gained stage experience as well as small TV roles after leaving college.

In 1996 he won the lead in his first film by Jonathan Glendening, La Belle Dame Sans Merci. This was a short film of the poem by John Keats, and it won awards at various film festivals.

His big TV break came in 1999, playing Dr Sam Morgan in the ITV drama serial Peak Practice.

Between filming each series of Peak Practice, he found time to return to the stage with his wife Caroline Fitzgerald in an innovative and acclaimed play Monogamy. Joseph and Caroline met in 1997 whilst starring in Ned Sherrin’s Salad Days. Monogamy provided a chance to utilise the production company set up by Joseph and Stuart Mullins in 1998, Pursued By A Bear.

After 2 years in Peak Practice, a dramatic storyline marked Joseph’s exit from the show. ‘They were keen for me to stay but I’m only 26 and I felt it was too soon in my career to be in one show for a long time,’ he explained at the time.

Next on the agenda was a return to the stage, with theatre production company Shared Experience in Mill On The Floss, which, after a run in the west end, was taken on tour. America and China were just two of the countries Joseph was looking forward to visiting with the play. ‘It’s going to be fantastic because I’m not very well travelled at all,’ said Joseph, ‘I’ve only been abroad three times, on holiday, so I can’t wait.’ (January 2001) TV Times.

The success of Mill On The Floss was followed by another touring production, directed by Paul Miller in 2001. Four Knights In Knaresborough, a darkly comic drama, was originated by New Vic Workshop at the Tricycle Theatre in London, where it opened to public and critical acclaim.

Joseph then returned to Shared Experiences as Robert in The Clearing, being directed by Polly Teale again, in 2002. A one man show also in 2002, The Lifted Veil, won Joseph a Hamilton Deane award for best dramatic presentation.

Two productions at the Royal Exchange Theatre in Manchester followed. The Seagull and Cold Meat Party both performed in Rep.

Joseph remained extremely busy throughout 2002/3, spending a few months on the popular BBC soap East Enders as character Jason James.

Said Joseph of his East Enders time; “Bizarrely I did a few months on East Enders and I had one week of my life when I found out what those poor buggers go through. I was only on the box for about seven weeks where I had a fling with the ugly Slater sister. But I was on TV for just long enough and I was on the Tube and realised that one person was clocking me and I thought 'that's okay' and by the time I looked back up the entire carriage was looking at me. It was like someone put a lightbulb above your head saying 'you saw this twit on telly last night'. And it was my last episode on telly the next day and it was gone, but what must it be like if you're on all the time?"

In 2003 he was nominated for the RSC Ian Charleston award. For "best classical actor under 30" it was for his role as Orlando, in Peter Hall's acclaimed As You Like it.

The Royal Shakespeare Company beckoned and Joseph took roles in 3 of the plays from The Spanish Golden Age Season in 2004/5, and impressed Lawrence Boswell the season director who declared; “Joe Millson, who is playing the male lead in my show (Dog in the Manger) and Nancy's (House of Desires) is a very exciting actor. He was recently in Sir Peter Hall's As You Like It for which he has been nominated for an Ian Charleson Award. I can see him playing other leading roles for the Royal Shakespeare Theatre in the near future if that’s what he wants."

As well as a memorable guest television role in the Channel 4 series Ghost Squad in 2005, there were lead roles notably as Banquo in the BBC’s Macbeth, in 2005 and Lord Byron in The Romantics in 2006.

A highlight for Joseph was appearing with Steven Berkoff in Richard II in 2005 "That was fantastic,'' he said. "He called me Phil for the entire run and it became such a running joke among the company during notes sessions that I never dared tell him! I worked at the National for Marianne Elliott, who also directed Much Ado, and through most of it I was able to be at home with the children."

Joseph then returned to the Royal Shakespeare Company in 2006 to take highly acclaimed lead roles as The Bastard in King John and as Benedick, in a superlative production by Marianne Elliot, of Much Ado About Nothing. He said: "I auditioned for all the season's companies because I wanted to come back. The only qualms I had were because we're a single-income family and, contrary to what most people believe, we don't actually get paid very much.''

In recent years, Joseph has gained a huge number of outstanding reviews, and has been compared to John Cleese and Kevin Kline for his outstanding comic timing and ability to “blend romantic dash with comic absurdity.” From reading the reviews, it is clear that Joseph is a favourite with a number of influential critics.

The end of 2006 remained extremely busy for Joseph. The London premier of Casino Royale was in November. A major big screen production, Joseph was cast as Carter, a fellow MI 6 operative of James Bond, in a brief scene that allowed him to perform his own stunt but left him with a cracked collar bone .

Much Ado About Nothing transferred to London in December for a month long, sell out run, at the Novello Theatre. The show garnered more fantastic reviews and won Tamsin Grieg an Olivier Award as best actress in February 2007.

Joseph landed a major role as Alan Jackson in a brand new BBC TV show that aired on New Years Day 2007, called The Sarah Jane Adventures. Positive reviews for the Doctor Who spinoff , helped ensure that Joseph was filming the full series during the Spring of 2007. He says he is such a fan of Doctor Who and was "thrilled to be doing it. And it is nice to be doing something my kids can watch".

The start of 2007 saw Joseph in the Isle of Man filming a four part mini-series called Talk To Me. Written by Danny Brocklehurst and co-starring Max Beesley, it aired on ITV 1 throughout June 2007.

A brief return to the stage to do some "strange 10 minute plays" at the Latitude Festival, for the Bush Threatre, in July, was followed in August by a cameo role in friend Nick Moran's film Telstar

As the Sarah Jane Adventures aired on CBBC at the end of September 2007 to great reviews ; Joseph was busy on stage at the Hampstead Theatre, before going straight on to making a film with Mackenzie Crook called Abrahams Point.

A return to the stage saw the end of a very successful 2007 and start of 2008 in the role of Prince Charming, in the panto Cinderella, written by Stephen Fry at the Old Vic Theatre.

At the end of Cinderella's run in January 2008, Joseph was filming S.N.U.B! before going on to film an episode of Midsomer Murders called "Days Of Misrule", and an episode of Harley Street. Short stage runs of Fear and Misery at the Royal Court and Possessed the Oxford Playhouse followed in April.

Before tackling Hamlet in Stafford in the summer to outstanding reviews; "a very short run but good to get a first go at that monster part out of my system", Joseph filmed 2 episodes of the second series of the Sarah Jane Adventures.

The latter part of summer 2008 saw Joseph complete filming on further lead guest roles in episodes of Survivors and Ashes to Ashes for the BBC, as well as a Radio 4 series Brief Lives, which were all broadcast on the BBC.

2009 started with a return to the stage in the acclaimed Tom Stoppard play Every Good Boy Deserves Favour at the National Theatre.

This was followed by numerous audio recordings; BBC radio plays Maud, Threepenny Opera and The Man In Black and a recording of the role of Raoul for the concept album Love Never Dies (Phantom Of The Opera sequel).

Joseph was cast as the role of Handley in the BBC 4 biopic Enid  which is due to be broadcast in the autumn of 2009.

Once filming was completed, Joseph started rehearsals for the role of Oberon in The Fairy Queen at Glyndebourne. Being staged over the summer 2009, the Opera was also broadcast on BBC Radio 3.

Before returning to the stage at the Almeida Theatre, in September  2009 in the production Judgement Day, Joseph was filming the Chris Crow directed Devil's Bridge in Wales and a Channel 4 comedy pilot Campus, which aired in November 2009.

After a run in the new play The Priory at the Royal Court Theatre in November / December  2009, Joseph started rehersals for the stage role of Raoul in Love Never Dies, which opened in March 2010 at the Adelphi Theatre, London.

A BBC pilot Reunited, filmed in March 2010, aired in June 2010. The Channel 4 comedy Campus was picked up for a full series and started filming at the beginning of July, with Joseph filming by day and on stage by night.