Joseph will join Guy Armitage in the centre, with Kieran Low joining Bryn Evans in the second-row and Mike Mayhew again starting at hooker.
Cardiff Blues director of rugby, Phil Davies, has named a line-up depleted due to international call-ups.
The Blues have no chance of making the LV= Cup knockout stages and are without Wales trio Sam Warburton, Jamie Roberts and Leigh Halfpenny.
Jason Tovey, Rhys Patchell and Michael Paterson all start for the home side.
Cardiff Blues: 15 Jason Tovey, 14 Owen Williams, 13 Gavin Evans (capt), 12 Dafydd Hewitt, 11 Harry Robinson, 10 Rhys Patchell, 9 Alex Walker, 8 Robin Copeland, 7 Thomas Young, 6 Michael Paterson, 5 James Down, 4 Cory Hill, 3 Benoit Bourrust, 2 Rhys Williams, 1 Nathan Trevett.
Replacements: 16 Kristian Dacey, 17 Sam Hobbs, 18 Taufa'ao Filise, 19 Luke Hamilton, 20 Rory Watts-Jones, 21 Lewis Jones, 22 Ceri Sweeney, 23 Chris Czekaj.
London Irish: 15 Tom Homer, 14 Topsy Ojo, 13 Jonathan Joseph, 12 Guy Armitage, 11 Marland Yarde, 10 Shane Geraghty (c), 9 Pat Phibbs, 8 Chris Hala'ufia, 7 Jebb Sinclair, 6 Matt Garvey, 5 Bryn Evans, 4 Kieran Low, 3 Halani Aulika, 2 Mike Mayhew, 1 Max Lahiff.
Replacements: 16 Davey McGregor, 17 Jerry Yanuyanutawa, 18 Leo Halavatau, 19 James Sandford, 20 Alex Gray, 21 Steven Shingler, 22 Ian Humphreys, 23 Jack Moates.
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The Barbarians are one of the top invitational rugby sides with a long history and classic rugby jersey.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Lions get ready for their matches with this green training jersey. It's what the players wear. Get in the Gear!
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Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
The Lions are ready to get their Australia tour underway. They arrive in Perth on Monday.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.