In the Beginning, he started in a two-man mime show with Harry Jones.  Denis was 18, but the title is unknown to me:-)
Metamorphosis - 1969 - Round House Theatre and the Hampstead Theatre Club.

Flowers - 1971 - Traverse - Starring the famous mime artist Lindsey Kemp.  Legend has it that when Kate Bush saw this play; it changed the way she approached her music, more visual and performance driven.
Hair - Touring company through Amsterdam and Oslo presented by the Cambridge Theatre Company.
Blow Job - Portable Theatre Group - Written By Snoo Wilson
England's Ireland - Opened 1 October, 1972 - Royal Court Theatre - Portable Theatre Group - Directors David Hare and Snoo Wilson - Starred Peter Adair, Tim Curry, Timothy Davies, Denis Lawson, Stanley McGeagh, Walter Monagle, Fidelma Murphy, Wesley Murphy, Dennis O'Neal, Fianuala O'Shannon and Jeremy Wilkin
The Royal Hunt of the Sun - Denis played Felipillo
Sarah B. Divine - Jeanetta Cochrane Theatre in London - Starred Patricia Quinn (Magenta in TRHPS) and based on the life of Sarah Bernhardt.
Jack and the Beanstalk - Dec. 22, 1973 to Jan. 26, 1974 - Cambridge Theatre Company
Twelfth Night - Oct. 1973 through 1974 - Cambridge Theatre Company production for The Ashcroft Theatre, Croydon - Starring: Diane Fletcher, Denis Lawson, Roger Rees, Zoë Wanamaker.
She Stoops to Conquer - February, 1974 - Cambridge Theatre Company production for The Ashcroft Theatre, Croydon - Cast: Diane Fletcher, Denis Lawson, Roger Rees, Zoë Wanamaker.
Candida - Nov. 20 to Dec. 14, 1974 -The Palace Theatre in Watford - Originally written by George Bernard Shaw.
Joseph and the Amazing Technicolor Dreamcoat - Leeds Playhouse
Mrs. Grabowski's Academy - Royal Court Theatre
Kidnapped for Christmas - Shaw Theatre
We Can't Pay, We Won't Pay - Half Moon Theatre
Cool Million - Half Moon Theatre - Denis co-starred opposite Patricia Quinn.
Jill & Jack - Created by Jack Osbourne
50 Words - Bits of Lenny Bruce (also called An Evening with Lenny Bruce) - 1975-76 - Kings Head Theatre and the Embassy Club - He played a variety of parts.
The Dog Ran Away - Oct., 1977 - Hampstead Theatre
Censored Scenes from King Kong - 1978 - Open Space Theatre
The Enemy Within - Thorndike, Half Moon and Albery Theatres
Leatherhead - Half Moon and Albery Theatres
Romeo and Juliet - Denis starred as Romeo.
The Greenish Man - 15th Nov. to 9th Dec., 1979 - Bush Theatre

Pal Joey - Opened in 4 August, 1980 and 26 September, 1980 - Half Moon and Albery Theatres
Mr. Cinders - Opened 5th January, 1983 - King's Head and the FortuneTheatres
The Lucky Chance - 10th July, 1984 - Royal Court Theatre
Have You Met Miss Jones? - Also starring Claire Moore - Written by Rodgers and Hart.
Lend Me a Tenor - Opened 6th March, 1986 - Globe Theatre
Ashes - Opened 20th November, 1986 and 3rd January, 1987 - Bush Theatre - Co-starring Sheila Gish.
The Importance of Being Earnest - Opened 11th September, 1987 - Royalty Theatre
The Film Society - Played 4th-27th February, 1988 - Hampstead Theatre

Volpone - Presented from 29th March to 5th April, 1990 - Almeida Theatre
Lust - Opened 19th July, 1993 - Theatre Royal in Haymarket
Oleanna - Opened in 1994 at the Duke of York Theatre - Directed by Harold Pinter, Denis, replacing David Suchet, played John, a professor who is accused of sexual harassment by a female student.
Lust - Opened in 1995 at the Walnut Street Theatre in Philadelphia and then in the John Houseman Theatre in New York.

Still trying to place:
City Delights - Opened at the Oxford Playhouse and transferred to the Hammersmith Lyric the following year.  I have no clue what it is about, but it co-starred Mike Berry.
denis lawson dennis lawson sheila gish lou gish kay curram ewam mcregor scotland movies films tv director stage television bbc star wars wedge antilles star
denis lawson dennis lawson sheila gish lou gish kay curram ewam mcregor scotland movies films tv director stage television bbc star wars wedge antilles star