Luton and Stansted are the closest airports to north London. Luton via Thameslink to St Pancras is fastest for northwest London. Stansted via Tottenham Hale is best for northeast London.
North London is best served by Luton (northwest) and Stansted (northeast). Luton's DART + Thameslink reaches St Pancras in ~40 minutes — ideal for Camden, Islington and King's Cross. Stansted Express to Tottenham Hale connects to the Victoria Line for Finsbury Park, Seven Sisters and Walthamstow. Heathrow is also viable for northwest London (Harrow, Wembley) but is further away.
Here is how the airports compare for north London:
Luton Airport is north of London. The DART automated rail link (5 minutes, £4.90) connects to Luton Airport Parkway station, where Thameslink trains run to St Pancras (~30 min), West Hampstead and Kentish Town. From St Pancras, Camden, Islington and King’s Cross are walking distance or a short bus ride. Total door-to-door to Camden: ~45 minutes.
Stansted Airport is northeast of London. The Stansted Express serves Tottenham Hale (~40 min), connecting to the Victoria Line for Finsbury Park, Seven Sisters and Walthamstow. For Hackney, change at Tottenham Hale for Overground or bus. Total door-to-door to Finsbury Park: ~55–65 minutes.
Luton. The DART rail link takes ~5 minutes to Luton Airport Parkway, then Thameslink reaches St Pancras in ~30 minutes — about 40 minutes in total. Camden is a 10-minute walk or 5-minute bus from St Pancras.
Yes but not ideal. Piccadilly Line to north London (Finsbury Park, Wood Green) takes 60–75 minutes. Only use Heathrow if your route is not served by Luton or Stansted.