The 32-year-old, who has signed for the club to play in the Vitality Blast that starts next week, played for the second team in their Second XI T20 Central Group double header against Gloucestershire at Wantage Road.
And the former Australia T20 and ODI star quickly got into his big-hitting stride.
Having arrived in the UK on Sunday, Lynn shook off his jetlag to make 48 from 34 balls in the opening three-run defeat, before hammering 73 from 42 balls to set up a 22-run win in the second.
Lynn hit four sixes in the opener but was particularly brutal in the second match, thumping seven sixes and dispatching a couple of balls into nearby gardens as the IIs posted 187 for six in their 20 overs.
Support for Lynn came from Saif Zaib (36no from 18), Harry Gouldstone (25 from 19) and James Sales (25 from 23).
Gloucestershire were then restricted to 165 for six, with Sales claiming three for 33, and seam bowler Nathan Buck conceding just 18 from his four overs.
In the earlier match, Ian Cockbain scored 105 not out for the visitors as they made 185 for three.
And although Northants looked well set to win at 138 for two in the 16th over, they fell short at 182 for five to lose by three runs.
Supporting Lynn in that match were Charlie Thurston (44 from 43) and Zaib (34 from 19).
Lynn is due to again play for Northants IIs as they travel to Taunton for another double header against Somerset on Thursday.
Northants Steelbacks begin their Blast campaign next Thursday night (May 26) when they travel to Birmingham Bears, before hosting Durham at the County Ground 24 hours later.