Beattie has agreed a three-year deal and will join from West Brom for a club-record undisclosed fee while Trundle, a cult hero in south Wales following a previous spell with the Swans, has joined on loan from Bristol City until January 1.
The pair's arrival is a timely boost for manager Paulo Sousa who is currently without a number of first-team players.
Leading scorer Stephen Dobbie is out with a hip injury while captain Garry Monk, defender Angel Rangel and striker Gorka Pintado are all suspended following their dismissals in Tuesday night's Carling Cup defeat to Scunthorpe.
Another new striker, Besian Idrizaj, is struggling with a thigh strain but Joe Allen (hamstring), Ferrie Bodde (knee) and Fede Bessone (groin) are nearly fit.
Darren Pratley (shoulder) and Thomas Butler (hernia) are definitely out.
Watford striker Danny Graham faces a late fitness test ahead of the trip.
The summer signing from Carlisle, who has scored two goals so far this season, suffered a knee injury during Tuesday night's 2-1 Carling Cup defeat at Leeds and will be assessed closer to kick-off.
With Nathan Ellington still struggling with a knee injury and Tommy Smith leaving to join Portsmouth, the Hornets could find themselves desperately short of numbers in attack.
Youngsters Marvin Sordell - who scored at Elland Road - and Liam Henderson may figure alongside Will Hoskins at the Liberty Stadium.
Winger Jobi McAnuff, who was thought to have missed out in midweek with a back injury he suffered against Nottingham Forest, joined Reading on Thursday.
Sporting Life