Television:
* Game of Thrones (2016-2019) as Qyburn, the Master of Whisperers
* The Crown (2016-2020) as Harold Macmillan
* Endeavour (2014-2020) as Chief Superintendent Reginald Bright
* Wolf Hall (2015) as Thomas Cromwell
* The Hollow Crown (2012-2016) as Cardinal Wolsey
* The Hour (2011-2012) as Hector Madden
* Spooks (2002-2011) as Harry Pearce
* Midsomer Murders (1997-present) as various roles
Film:
* The King's Speech (2010) as Lord Chamberlain
* The Imitation Game (2014) as Commander Denniston
* The Woman in Black (2012) as Mr. Bentley
* Pride & Prejudice (2005) as Mr. Collins
* Shakespeare in Love (1998) as Lord Chamberlain
* The Importance of Being Earnest (2002) as Reverend Chasuble
This is not an exhaustive list, but it represents some of Lesser's most significant and well-known roles. He has also appeared in numerous other television series, mini-series, and films, often portraying historical figures or characters of authority.
You can find a more comprehensive list of his filmography on websites like IMDb or Rotten Tomatoes.