The move will reunite him with Top Up TV chairman David Chance, with whom Hytner worked at BSkyB before moving on to the then Channel 5, ITV, where he was marketing director, and Barclays.
Chance said: "We have ambitious plans for the months and years ahead and today's announcement underlines this."
Top Up TV was founded in 2003 to offer Freeview customers additional channels on a subscription basis. It carries 21 channels including Paramount Comedy, MTV, Disney, and the Cartoon Network. From this season, it is adding Setanta Sports. It is facing the prospect of more direct competition from Sky, which has revealed plans to launch its own pay-TV channels on Freeview, but is having to wait for Ofcom to consult on its move.
Hytner said: "The opportunity to use the experience that I have built up over recent years at Barclays and to help develop the Top Up TV business was one I could not resist. I have known David and Nick Markham, Top Up TV's CEO, for many years and I very much look forward to the challenges ahead as we look to fulfil the extraordinary potential that Top Up TV represents."
At Barclays, Hytner's departure will lead to Deanna Oppenheimer, chief executive of the UK retail bank, taking charge of the marketing department before making a decision on a long-term structure.
McVitty said she was unwilling to speculate on whether Barclays would be seeking a direct replacement for Hytner, who she said had done a "fabulous job" and would be missed.
She added Hytner had brought in talented people such as Sarah Wise, heading up above-the-line work, and David Jeppersen, heading up direct marketing.
Barclays is currently pursuing a major transformative deal with the attempted takeover of Dutch global bank ABN Amro, but is facing stiff competition from a consortium led by rival Royal Bank of Scotland.
Hytner is returning to the media sector after three years at Barclays, before which he helped form the image of a single ITV out of the Granada/Carlton merger.
The Hytner CV
2007 Commercial director, Top Up TV
2004 Group brand & UK banking marketing director, Barclays
2001 Commercial and marketing director, ITV
1996 Marketing director, Channel 5
1994 Marketing director, BSkyB
Prior to Sky, Hytner worked at Sega and before that Coca Cola.