The 30-year-old played for Sheffield Eagles against Paris St Germain in the first ever Super League game in 1996, and will begin his four-month testimonial at the Rhinos with a game against Huddersfield Giants on Friday.
Senior made his Lions debut in 1996 when he took on Fiji in Nadi, and won his 30th cap against Australia in Brisbane in last autumn’s Gillette Tri-Nations series, saying, "I see it as a great milestone to reach 30 caps."
With four more test matches before the end of the season, Senior will have the opportunity to go fifth in the all-time lost of Great Britain appearances, overtaking both Martin Offiah and Daryl Powell.
The testimonial match against Huddersfield will be played in partnership with Giants full-back Paul Reilly; but unlike Reilly, who will retire at the end of the season, Senior wants to continue in club rugby.
"I've two years left at Leeds and then I'll take it year by year depending on the body," he said. "It's been superb. It's a short career and you are a long time retired so you have to enjoy every minute of it. My goal is to remain a regular first teamer for at least the next two years."