In February 1796, the 52nd movded from Ceylon to Madras and then to Tanjore. It was here that Lawrence joined the 52nd on 1 Aug 1796 as an Ensign, replacing Alexander MacDonald who was promoted to the 72nd Regiment of Foot. 
On 1 January 1797 Lawrence was promoted to Lieutenant replacing Lieutenant William Wardrobe who was promoted to Captain-Lieutenant who in turn replaced Edmund Burke who was promoted to Captain who inturn replaced Irwine who was "removed to the Royal Garrison Battalion". Three other ensigns were also promoted on this date, Eccles McConnegal, John Steeney and John Ross. . The promotion was not announced in the London Gazette until a year later, presumably because of the communication lag
On 18 October 1797 the Regiment was under orders to return to England, the effective men (ie those who were non-commissioned) were drafted to other Regiments, primarily the 77th and 80th Foot Regiments and received 3 guineas if they did so .
On 1 November 1797 he was seconded to the 32nd Regiment. 
The 52nd were to be moved back to England and on 16 Feb 1799 Lawrence exchanged with Lieutenant William Fennel of the 33rd Regiment. Other Lieutenants, Thomas Reed (of the 52nd), William Fraser (36th), Nathaniel B Tucker and John Whitlies (both of the 72nd) did likewise. 
The story continues on the The 33rd Regiment pages.
 Source: London Gazette No.14004 April 25 1797. "Lawrence O'Hara, Gent to be Ensign vice Macdonald promoted in the 72nd Foot."
 Source: The Asiatic Journal and Monthly Register for British India and Its Dependencies (1801) p131: on Google Books
Capt. Lieutenant E. Burke to be captain of a company, vice Irwine, removed to the Royal Garrison Battalion. Dec 4 1795.
Lieut. W Wardrobe to be captain-lieutenant, vice Burke, promoted Ditto.
Ensign Laurence O'Hara to be lieutenant, vice Wardrobe, promoted Jan 1 1797
Ensign E McConnegal to be lieutenant vice Mackenzie, deceased Jan 2 1796
Ensign J Steeney to be lieutenant by purchase vice Brown, promoted 41st Foot Jan 6 1797
Ensign John Rofs from 36th foot to be lieutenant without purchase vice Hicks who resigned May 8 1797
William Frith grant to ensign by purchase vice Armstrong, promoted in 71st Foot Aug 2 1797
E W Manoury gent. to be ensign by purchase vice Stoney promoted Aug 3 1797
Lionel Hook gent. to be enfign vice McConnegal promote Dec 20
Ensign J T Sattherthwaite from 76 foot to be ensign vice O'Hara promoted Jan 1 1797
M M Madden gent to be ensign vice Bird who resigns Jan 3
 Source: PRO/WO12/5025-5029
 Source: Historical Record of the Fifty-Second Regiment (Oxford Light Infantry) WS Moorsom (1860).
 Source: London Gazette No. 15108 16th February 1799.
 Source: London Gazette Issue 14078 published on the 30 December 1797