He assisted Jeff Lynne and Richard Tandy in writing the string arrangements for the studio albums Eldorado, Face the Music, A New World Record, Out of the Blue, Discovery and Xanadu.

In 1983 he returned to arranging and conducting the strings on the Secret Messages album, and in 1986 he played keyboards again with the band on their small number of live dates.

Upon Part II's rebranding as The Orchestra in 2000, Clark (now a full-time member) remained with the group, his involvement continuing until his death in 2021.

In 1985, he again worked with Renaissance singer Annie Haslam and the band's lyricist Betty Thatcher with the RPO to produce the album "Still Life".

In 2011 Louis Clark was made president of the English Pops Orchestra, and returned to performing Hooked on Classics 'LIVE' with the EPO using many of the players that recorded the original albums.

"[6][5] Besides ELO, Louis Clark worked as an arranger for many other rock and pop artists: With Roy Orbison With Ozzy Osbourne With Roy Wood With Kelly Groucutt With America With Kiki Dee With Carl Wayne With Juan Martin With Asia With Mike Berry With Simone With Renaissance With City Boy Among others are UB40, Jon Spencer, Iris Williams and more recently Air Supply.